The Revelation in the New Testament by St. John is a good start to be considered about the early Church belief in the doctrine of intercession of the Saints. With this vision of St. John, it foreshadow the new Jerusalem temple where in the Catholic mass, the Priest make an offering of incense for prayers and worship to God.
Pope Clement of Rome and Saint Policarp says with reference from:
The Ante-Nicene-Fathers Vol.1, The Apostolic Fathers with Justin Martyrs & Irenaeus by Philip Schabb
The Epistle of Polycarp to the Philippians337, A.D 65-100-155
Chapter XII.—Exhortation to various graces. For I trust that ye are well versed in the Sacred Scriptures, and that nothing is hid from you; but to me this privilege is not yet granted.404 It is declared then in these Scriptures, “Be ye angry, and sin not,”405 and, “Let not the sun go down upon your wrath.”406 Happy is he who remembers407 this, which I believe to be the case with you. But may the God and Father of our Lord Jesus Christ, and Jesus Christ Himself, who is the Son of God, and our everlasting High Priest, build you up in faith and truth, and in all meekness, gentleness, patience, long-suffering, forbearance, and purity; and may He bestow on you a lot and portion among His saints, and on us with you, and on all that are under heaven, who shall believe in our Lord Jesus Christ, and in His Father, who “raised Him from the dead.”408 Pray for all the saints. Pray also for kings,409 and potentates, and princes, and for 36 those that persecute and hate you,410 and for the enemies of the cross, that your fruit may be manifest to all, and that ye may be perfect in Him. It
ANF01. The Apostolic Fathers with Justin Martyr and Irenaeus Philip Schaff
The First Epistle of Clement to the Corinthians, A.D. 30-100
Chapter LVI.—Let us admonish and correct one another. Let us then also pray for those who have fallen into any sin, that meekness and humility may be given to them, so that they may submit, not unto us, but to the will of God. For in this way they shall secure a fruitful and perfect remembrance from us, with sympathy for them, both in our prayers to God, and our mention of them to the saints.247 Let us receive correction, beloved, on account of which no one should feel displeased. Those exhortations by which we admonish one another are both good [in themselves] and highly profitable, for they tend to unite248 us to the will of God.
Please see below bible verses and the corresponding commentaries.
8 And when he had opened the book, the four living creatures and the four and twenty ancients fell down before the Lamb, having every one of them harps and golden vials full of odours, which are the prayers of saints.
Commentary: Irenaeus of Lyons A.D. 202
Since, therefore, the name of the Son belongs to the Father, and since in the omnipotent God the Church makes offerings through Jesus Christ, He says well on both these grounds, "And in every place incense is offered to My name, and a pure sacrifice. "Now John, in the Apocalypse, declares that the "incense "is "the prayers of the saints."
Revelation 8:3 RHE
3 And another angel came and stood before the altar, having a golden censer: and there was given to him much incense, that he should offer of the prayers of all saints, upon the golden altar which is before the throne of God.
Revelation 8:4 RHE
4 And the smoke of the incense of the prayers of the saints ascended up before God from the hand of the angel.
Commentary: George Leo Haydock A.D. 1849 Stood before the altar, having a golden censer. In the visions is an allusion to the tabernacle and its parts. The altar of perfumes was in the sanctum, and here the golden altar is said to be before the throne of God. The incense from the censer is said to be the prayers of all the Saints, which the Angel offered up. The altar seems to signify our Saviour Christ, as the prayers of all the faithful are always made through the merits of Christ, our only chief Mediator or Redeemer. By the fire cast upon the earth, (ver. 5.) is signified the fire of divine charity, now to be exercised by the ways of justice, to draw persons to their conversion by punishments. (Witham) We may observe both in this and other places of the Apocalypse, that St. John makes continual allusions to what was done in the temple of Jerusalem, for which he gives us symbolical reasons. Thus on the present occasion, the incense which was offered morning and evening in the temple, on the golden altar, is represented as done here in heaven. (Calmet)
1 Timothy 2:1 RHE
1 I desire therefore, first of all, that supplications, prayers, intercessions and thanksgivings be made for all men:
Commentary: George Haydock
Intercessions, as in the Protestant translation. If men's intercessions to God in favour of others, are no injury to Christ, as our mediator, how can it be any injury to Christ for the Angels and saints in heaven to pray or intercede to God for us? (Witham) St. Augustine writes thus on this verse: By supplications are meant what are said before the consecration. By prayers, are what are said in and after the consecration and communion, at mass, including the Pater Noster; which St. Jerome also says, our Lord taught his apostles to recite at the daily sacrifice of his body. (lib. iii. contra Pelag. chap. 5) By intercessions, what are said after the communion: and by thanksgivings, what both the priest and people give to God for so great a mystery then offered and received. (ep. 50. ad Paulin.) See St. Chrysostom on this place.
As the following passages show, the early Church Fathers not only clearly recognized the biblical teaching that those in heaven can and do intercede for us, but they also applied this teaching in their own daily prayer life.
Hermas “[The Shepherd said:] ‘But those who are weak and slothful in prayer, hesitate to ask anything from the Lord; but the Lord is full of compassion, and gives without fail to all who ask him. But you, [Hermas,] having been strengthened by the holy angel [you saw], and having obtained from him such intercession, and not being slothful, why do not you ask of the Lord understanding, and receive it from him?’” (The Shepherd 3:5:4 [A.D. 80]).
Clement of Alexandria “In this way is he [the true Christian] always pure for prayer. He also prays in the society of angels, as being already of angelic rank, and he is never out of their holy keeping; and though he pray alone, he has the choir of the saints standing with him [in prayer]” (Miscellanies 7:12 [A.D. 208]).
Origen “But not the high priest [Christ] alone prays for those who pray sincerely, but also the angels . . . as also the souls of the saints who have already fallen asleep” (Prayer 11 [A.D. 233]).
Cyprian of Carthage “Let us remember one another in concord and unanimity. Let us on both sides [of death] always pray for one another. Let us relieve burdens and afflictions by mutual love, that if one of us, by the swiftness of divine condescension, shall go hence first, our love may continue in the presence of the Lord, and our prayers for our brethren and sisters not cease in the presence of the Father’s mercy” (Letters 56:5 [A.D. 253]).
Anonymous “Atticus, sleep in peace, secure in your safety, and pray anxiously for our sins” (funerary inscription near St. Sabina’s in Rome [A.D. 300]).
“Pray for your parents, Matronata Matrona. She lived one year, fifty-two days” (ibid.).
“Mother of God, [listen to] my petitions; do not disregard us in adversity, but rescue us from danger” (Rylands Papyrus 3 [A.D. 350]).
Methodius “Hail to you for ever, Virgin Mother of God, our unceasing joy, for to you do I turn again. . . . Hail, you treasure of the love of God. Hail, you fount of the Son’s love for man” (Oration on Simeon and Anna 14 [A.D. 305]).
“Therefore, we pray [ask] you, the most excellent among women, who glories in the confidence of your maternal honors, that you would unceasingly keep us in remembrance. O holy Mother of God, remember us, I say, who make our boast in you, and who in august hymns celebrate the memory, which will ever live, and never fade away” (ibid.).
“And you also, O honored and venerable Simeon, you earliest host of our holy religion, and teacher of the resurrection of the faithful, do be our patron and advocate with that Savior God, whom you were deemed worthy to receive into your arms. We, together with you, sing our praises to Christ, who has the power of life and death, saying, ‘You are the true Light, proceeding from the true Light; the true God, begotten of the true God’” (ibid.).
Cyril of Jerusalem “Then [during the Eucharistic prayer] we make mention also of those who have already fallen asleep: first, the patriarchs, prophets, apostles, and martyrs, that through their prayers and supplications God would receive our petition” (Catechetical Lectures 23:9 [A.D. 350]).
Hilary of Poitiers “To those who wish to stand [in God’s grace], neither the guardianship of saints nor the defenses of angels are wanting” (Commentary on the Psalms 124:5:6 [A.D. 365]).
Ephraim the Syrian “You victorious martyrs who endured torments gladly for the sake of the God and Savior, you who have boldness of speech toward the Lord himself, you saints, intercede for us who are timid and sinful men, full of sloth, that the grace of Christ may come upon us, and enlighten the hearts of all of us so that we may love him” (Commentary on Mark [A.D. 370]).
“Remember me, you heirs of God, you brethren of Christ; supplicate the Savior earnestly for me, that I may be freed through Christ from him that fights against me day by day” (The Fear at the End of Life [A.D. 370]).
The Liturgy of St. Basil “By the command of your only-begotten Son we communicate with the memory of your saints . . . by whose prayers and supplications have mercy upon us all, and deliver us for the sake of your holy name” (Liturgy of St. Basil [A.D. 373]).
Pectorius “Aschandius, my father, dearly beloved of my heart, with my sweet mother and my brethren, remember your Pectorius in the peace of the Fish [Christ]” (Epitaph of Pectorius [A.D. 375]).
Gregory of Nazianz “May you [Cyprian] look down from above propitiously upon us, and guide our word and life; and shepherd this sacred flock . . . gladden the Holy Trinity, before which you stand” (Orations 17 [A.D. 380]).
“Yes, I am well assured that [my father’s] intercession is of more avail now than was his instruction in former days, since he is closer to God, now that he has shaken off his bodily fetters, and freed his mind from the clay that obscured it, and holds conversation naked with the nakedness of the prime and purest mind” (ibid., 18:4).
Gregory of Nyssa “[Ephraim], you who are standing at the divine altar [in heaven] . . . bear us all in remembrance, petitioning for us the remission of sins, and the fruition of an everlasting kingdom” (Sermon on Ephraim the Syrian [A.D. 380]).
John Chrysostom “He that wears the purple [i.e., a royal man] . . . stands begging of the saints to be his patrons with God, and he that wears a diadem begs the tentmaker [Paul] and the fisherman [Peter] as patrons, even though they be dead” (Homilies on Second Corinthians 26 [A.D. 392]).
“When you perceive that God is chastening you, fly not to his enemies . . . but to his friends, the martyrs, the saints, and those who were pleasing to him, and who have great power [in God]” (Orations 8:6 [A.D. 396]).
Ambrose of Milan “May Peter, who wept so efficaciously for himself, weep for us and turn towards us Christ’s benign countenance” (The Six Days Work 5:25:90 [A.D. 393]).
Jerome “You say in your book that while we live we are able to pray for each other, but afterwards when we have died, the prayer of no person for another can be heard. . . . But if the apostles and martyrs while still in the body can pray for others, at a time when they ought still be solicitous about themselves, how much more will they do so after their crowns, victories, and triumphs?” (Against Vigilantius 6 [A.D. 406]).
Augustine “A Christian people celebrates together in religious solemnity the memorials of the martyrs, both to encourage their being imitated and so that it can share in their merits and be aided by their prayers” (Against Faustus the Manichean [A.D. 400]).
“At the Lord’s table we do not commemorate martyrs in the same way that we do others who rest in peace so as to pray for them, but rather that they may pray for us that we may follow in their footsteps” (Homilies on John 84 [A.D. 416]).
“Neither are the souls of the pious dead separated from the Church which even now is the kingdom of Christ. Otherwise there would be no remembrance of them at the altar of God in the communication of the Body of Christ” (The City of God 20:9:2 [A.D. 419]).
NIHIL OBSTAT: I have concluded that the materials presented in this work are free of doctrinal or moral errors. Bernadeane Carr, STL, Censor Librorum, August 10, 2004
IMPRIMATUR: In accord with 1983 CIC 827 permission to publish this work is hereby granted. +Robert H. Brom, Bishop of San Diego, August 10, 2004