There’s a two title that is stated in this verse “another Advocate” and “Spirit of Truth”.
In 1John2:1 the First Advocate is Jesus Chirst., the another Advocate & Spirit of Truth is the Holy Spirit that was not Incarnated but can dwell in human soul to manifest Her/His presence.
"My dear children, I write this to you so that you will not sin. But if anybody does sin, we have an advocate with the Father—Jesus Christ, the Righteous One."(1John2:1)
Or do you not know that your body is a temple of the Holy Spirit who is in you, whom you have from God, and that you are not your own?(1Corinthian6:19)
So, this passage in John14:16 tells us in reading that the “another Advocate” and “Spirit of Truth” is the same being or the same person.
Therefore, identifying who is the “another Advocate” would mean She/He is also the “Spirit of Truth”.
To identify who is the "Spirit of Truth" we can use the hint provided by Jesus in John5:36 as Jesus said to the Apostles you can testify too meaning the "Spirit of Truth" will give the Apostles & disciples the power & graces to testify.
But Jesus said there is one who will who testify to witness the "fullness of who He is" and "His redemptive works". This one is greater than John the Baptist.
"But I have a greater witness than that of John..."(John5:36)
Now Christian said this is the Abba Father, but considering the Wisdom of Jesus this will be an elementary discourse, Why? we all know the Abba Father cannot be compare to any creature even to John in terms of Infinite Greatness, Jesus is talking of "another person greater than John the Baptist.
And the big question is how can the Abba Father "testify" to the people of God, we have no "beatific vision". Jesus is clearly talking of a corporeal being that the Holy Spirit will "indwelt" to testify to the TRUTH.
If we study and search who is the possible person during Jesus time that is greater than John the Baptist, and even greater than all the Apostles & Disciples in the Upper Room.
The only question is it's testimony is hidden in the bible it remain a mystery for all of us.But, we are not left totally left in the dark, although the bible is not complete we have an Apostolic Tradition and Prophets(Approved Private Revelation) that is deposited to the Catholic Church. Like the Mysterious painting of St.Luke below referred to as achiropita—'made without hands, the painting is called "Advocata Nostra".
An Archangel testify that She is 'Full of Grace".(Luke1:28)
She said the "Mighty One had done great things for me..."(Luke1;49)
And Her mere greetings made John the Baptist leaped in the womb of Elizabeth, and the Holy Spirit sanctified John the Baptist and Elizabeth also was filled by the presence of the Holy Spirit that Overshadowed the Handmaid of the Lord.(Luke1:41)
4.She can give the testimony greater than John because She will witness from "womb to tomb" and the "Eternal Redemptive Mission of Jesus his beloved son'.
- Lastly, according to Church Fathers only Mary can explain the Mystery of the Holy Trinity because She lived a Trinitarian Life" in full by the power of the Holy Spirit forming Her a new creature as Her Spouse.
But the Catholic Church like Mary is a humble Church, they wait for God's Providence to give Her a title according to God's Will and timing.
Are we certain that all the Apostles & Disciples in the Upper Room never asked the Theotokos to "testify & witness to them who Jesus is and His Redemptive Mission"?
This is still a Mystery, but a Catholic Church proclaiming Mary as the Advocate in the Fifth Dogma by a Papal solemn definition will follow the identification of the "Spirit of Truth".
For now, the Catechism of the Catholic Church the “Spirit of Truth” and “‘Advocate/Paraclete” is identified as the Holy Spirit in CCC692.
692 When he proclaims and promises the coming of the Holy Spirit, Jesus calls him the "Paraclete," literally, "he who is called to one's side," ad-vocatus. "Paraclete" is commonly translated by "consoler," and Jesus is the first consoler. The Lord also called the Holy Spirit "the Spirit of truth."
Also, there’s one Article of Faith in the Catechism pointing to Mary’s title as Advocate.
969 "This motherhood of Mary in the order of grace continues uninterruptedly from the consent which she loyally gave at the Annunciation and which she sustained without wavering beneath the cross, until the eternal fulfillment of all the elect. Taken up to heaven she did not lay aside this saving office but by her manifold intercession continues to bring us the gifts of eternal salvation. . . . Therefore the Blessed Virgin is invoked in the Church under the titles of Advocate, Helper, Benefactress, and Mediatrix."
This Article of Faith is CCC692 & CCC969 has two person identified by Catholic Teaching as both Advocate, the Holy Spirit and Mary.
The Catholic Church thru Papal solemn definition will clear the meaning to harmonize this two article of faith.
Advocate. or Paraclete , one that pleads the cause of ... Spelling: (par-ak'-lay-tos)
Short Definition: an advocate, comforter, helper .
St.John Paul II the Great called Mary's powerful intercession as Maternal Mediation and below is the link on St. Jonh Paul II Teaching on CCC969
MARY HAS UNIVERSAL SPIRITUAL MOTHERHOOD
(Pope John Paul II)
Our Lady is mother of all humanity because she co-operated with faith, hope and charity in Christ’s work of restoring supernatural life to souls
The Blessed Virgin, "having entered the Father's eternal kingdom, closer to her divine Son and thus closer to us all, can more effectively exercise in the Spirit the role of maternal intercession entrusted to her by divine Providence", the Holy Father said at the General Audience of Wednesday, 24 September, as he discussed Mary's motherhood in the order of grace. He went on to explain the meaning of the Marian titles of Advocate, Helper, Benefactress and Mediatrix. Here is a translation of the Pope's catechesis, which was the 64th in the series on the Blessed Virgin and was given in Italian. - MARY HAS UNIVERSAL SPIRITUAL MOTHERHOOD
How about during Apostolic Times do the Apostles recognized Mary as their Advocate?
- Peter and Judas account
Peter and Judas both betrayed our Lord Jesus Christ but Peter seek Mary’s refuge and was able to rise up while Judas did not and eventually hang himself to death.
- St.James the Greater account in year 40AD “Our Lady of the Pillar Apparition”
St.James the Greater feel desolation in preaching the Gospel and Mary appears to him to strengthen and comfort him.
Note: This is an apparition not a bi-location, Mary does not appear in an ordinary human appearance, She was on top of a 6 foot Jasper Column accompanied by angels. Mary is above all men and angels were Her servants.
- Do all the Apostles recognize Mary as Advocate? St. Luke's painting speak louder than words.
Advocata Nostra, the oldest icon of Mary in Rome, at the Dominican Sisters Convent on Via Trionfale on Monte Mario. This icon can be traced back to its origin in Jerusalem, where tradition has it that it was painted by St Luke after the Resurrection, at the request of the apostles. But the tradition also states that after St Luke had sketched the outline, the image of Our Lady appeared on it. No human hand was involved. Such works are referred to as achiropita—'made without hands
From the 2000 years of the Catholic Church from Apostles, early Church Fathers, Church Fathers, Saints, Theologians and faithfuls all seeks and invoke Mary’s powerful intercession.
The Litany of Saints, all those names have a deep devotion to Mary as their Advocate.
Include also Popes and all the known Clergy from Cardinals, Bishops and Priests all had a lot to say about the Maternal Mediation of Mary.
But the 3 Giant Marian Saints who stood tall in pointing to Mary as the “another Advocate” are;
- St.Alphonsus Liguori
"In His eagerness to show you,mercy, God has given His Son as your Advocate. And then to make your confidence even stronger, He has given you "another Advocate', who obtains through her prayers whatever she asks.Go to Mary, and you will see salvation. -St.Alphonsus Ligouri
- St.Louis DeMontfort
God the Holy Spirit entrusted his wondrous gifts to Mary, his faithful spouse, and chose her as the dispenser of all he possesses, so that she distributes all his gifts and graces to whom she wills, as much as she wills, how she wills and when she wills. No heavenly gift is given to men which does not pass through her virginal hands. Such indeed is the will of God, who has decreed that we should have all things through Mary, so that, making herself poor and lowly,, and hiding herself in the depths of nothingness during her whole life, she might be enriched, exalted and honoured by almighty God. Such are the views of the Church and the early Fathers. (True Devotion to Mary)
- St.Maximillian Kolbe
“St. Kolbe teaches that Mary is the “quasi Incarnation of the Holy Spirit” meaning Mary is “Possessed”, Her thoughts, words and actions are perfectly and completely coming from the Holy Spirit.
The Holy Spirit And Mary
How About Church Magisterial Teaching and Documents, what does it says about Mary & the Holy Spirit?
Magisterial Documents: Mary and the Holy Spirit
Below are direct quotes from Post-Vatican II Magisterial Documents concerning the following themes. These teachings of the Catholic Church may prove useful to include in talks, in homilies or for research.
FASHIONED BY THE SPIRIT (HER WHOLE EXISTENCE)
Lumen Gentium, 1964
[Mary] fashioned by the Holy Spirit and formed as a new creature [cf. Germanus >of Constantinople, "Hom. in Annunt. Deiparae": PG 98, 328A, etc.] 56
Signum Magnum, 1967
prophetic canticle she had uttered under the inspiration of the Holy Spirit >[Magnificat] 3
She freely and earnestly heeded the interior promptings of the Holy Spirit at >all times. 16
her generous efforts under God's inspiration [see "fullness of grace" ahead] 21
General Catechetical Directory, 1971
The gift of Christ's Spirit is manifested in her in an altogether singular >manner, because Mary is "full of grace" (Lk 1, 28) and is "a model of the >Church." (LG, 63) 68
who was preserved from all stain of original sin,
who was freely and fully faithful to the Lord,
and who was assumed body and soul into heavenly glory,
the Holy Spirit has fully manifested his gift. 68
Behold Your Mother (USA), 1973
"fashioned by the Holy Spirit into a kind of new substance and a new creature." >(LG 56) 52
led by the Holy Spirit in everything (PO 18) 69
servant of the Spirit 106
The role of the Holy Spirit in the life of Mary is especially pertinent to our time. Mary of the Magnificat is, after Jesus himself, the supreme New Testament example of one who is led by the Holy Spirit. Not only the Magnificat, but Mary's whole life was a song of love inspired by the Holy Spirit. "Led by the Holy Spirit, she devoted herself entirely to the mystery of man's redemption." (PO 18) [Discussed under Mother of the Church] 118
Marialis Cultus, 1974
adorned her with gifts of the Spirit granted to no one else 25
Theological reflection and the liturgy have in fact noted how the sanctifying intervention of the Spirit in the Virgin of Nazareth was a culminating moment of the Spirit's action in the history of salvation. Thus, for example, some Fathers and writers of the Church attributed to the work of the Spirit the original holiness of Mary, who was as it were "fashioned by the Holy Spirit into a kind of new substance and new creature." (LG 56) 26
Gaudete in Domino, 1975
The attainment of such an outlook is not just a matter of psychology. It is also a fruit of the Holy Spirit. This Spirit, who dwells fully in the person of Jesus, made him during his earthy life so alert to the joys of daily life, so tactful and persuasive for putting sinners back on the road to a new youth of heart and mind! It is this same Spirit who animated the Blessed Virgin and each of the saints.
Redemptor Hominis, 1979
under the special influence of the Holy Spirit, this heart Final paragraph
Ephesus, 1550th Anniversary, 1981
In her there dawned the new humanity which with Christ was presented in the world in order to bring to completion the original plan of the covenant with God, broken by the disobedience of the first man. 4
Redemptoris Mater, 1987
[Calvary] And how powerful too is the action of grace in her soul, how all >pervading is the influence of the Holy Spirit and of his light and power! 18
The Virgin Mary in Intellectual and Spiritual Formation, 1988
"She is, at it were, fashioned and formed into a new creature" (LG 56) by the Holy Spirit. 8
Veritatis Splendor, 1993
Mary experiences, in perfect docility to the Spirit, the richness and the universality of God's love, which opens her heart and enables it to embrace the entire human race. 120
Tertio Millennio Adveniente, 1994
...and then in the whole of her life allowed herself to be guided by his interior activity, will be contemplated and imitated during this year above all as the woman who was docile to the voice of the Spirit, a woman of silence and attentiveness, a woman of hope who, like Abraham, accepted God's will "hoping against hope." (cf. Rom 4:18) 48
Catechism of the Catholic Church, 1994 Fidei Depositum, 1992
493 The Fathers of the Eastern tradition call the Mother of God "the All-Holy" (Panagia) and celebrate her as "free from any stain of sin, as though fashioned by the Holy Spirit and formed as a new creature." (LG 56) By the grace of God Mary remained free of every personal sin her whole life long.
722 The Holy Spirit prepared Mary by his grace. It was fitting that the mother of him in whom "the whole fullness of deity dwells bodily" (Col 2:9) should herself be "full of grace." She was, by sheer grace, conceived without sin as the most humble of creatures, the most capable of welcoming the inexpressible gift of the Almighty. It was quite correct for the angel Gabriel to greet her as the "Daughter of Zion": "Rejoice." (Cf. Zeph 3:14; Zech 2:14) It is the thanksgiving of the whole People of God, and thus of the Church, which Mary in her canticle (cf. Lk 1:46-55) lifts up to the Father in the Holy Spirit while carrying within her the eternal Son.
744 In the fullness of time the Holy Spirit completes in Mary all the preparations for Christ's coming among the People of God. By the action of the Holy Spirit in her, the Father gives the world Emmanuel, "God-with-us." (Mt 1:23)
Vita Consecrata, 1996
It is in the contemplation of the crucified Christ that all vocations find their inspiration. From this contemplation, together with the primordial gift of the Spirit, all gifts, and in particular the gift of the consecrated life, take their origin. After Mary, the mother of Jesus, it is John who receives this gift.. John is the disciple whom Jesus loved, the witness who together with Mary stood at the foot of the cross (cf. Jn 19:26-27) ... John, together with Mary, is among the first in a long line of men and women who, from the beginning of the church until the end, are touched by God's love and feel called to follow the Lamb (cf. Rv 14:1-5) (cf. Proposition 3). 23
Consecrated life looks to her as the sublime model of ... openness to the Spirit 28
Now, a Papal solemn definition on the Fifth Dogma proclaiming Mary as the Advocate looking on the 2000 history of the Church invoking the Maternal Mediation of Mary and highlighting the 3 solid teaching of this 3 giant Marian Saints one a Doctor of the Church and the other (St.Montfort ) also in the process of proclaiming a Doctor of the Church plus the voluminous Magisterial Teaching on Mary fashioned by the Holy Spirit and formed as a new creature (All Her Existence)
The Mystical and Espousal Union of Mary and the Holy Spirit which St.Kolbe called “quasi Incarnates” meaning Mary became the perfect image of the Holy Spirit would mean all the titles and salvific works of the Holy Spirit are done in perfect & complete cooperation of the Theotokos.
The proclamation of the Fifth Dogma with Papal Solemn definition of Mary's Role as Co-Redemptrix,Mediatrix, and Advocate will clear perfectly the passage on John14:16 and will harmonize the Church Official Doctrine on CCC692 & CCC969.
Mary as the "another Advocate"(St.Liguori Teaching; a Doctor of the Church), manifest the mission and salvific role of the Holy Spirit perfectly and completely as the "Spirit of Truth".****(St.Montfort & St.Kolbe's Teaching both advocate of Total Consecration to Mary).