According to Catholicism, were all 1st century Christians called “saints” by saints Paul, Jude, John etc, as they addressed all believers reading their New Testament writings as “saints”?
The short answer is yes, however he applied other terms to 1st century Christians as well.
Saint Paul, the Apostle of the Gentiles employed several terms by which the Followers of the Way were addressed, either by himself or employed by other including the term of saints.
In Acts 11:26, we see that the followers of Christ were called Christians.
The first recorded use of the term (or its cognates in other languages) is in the New Testament, in Acts 11 after Barnabas brought Saul (Paul) to Antioch where they taught the disciples for about a year, the text says: "[...] the disciples were called Christians first in Antioch." (Acts 11:26). The second mention of the term follows in Acts 26, where Herod Agrippa II replied to Paul the Apostle, "Then Agrippa said unto Paul, Almost thou persuadest me to be a Christian." (Acts 26:28). The third and final New Testament reference to the term is in 1 Peter 4, which exhorts believers: "Yet if [any man suffer] as a Christian, let him not be ashamed; but let him glorify God on this behalf." (1 Peter 4:16)
Then there are the disciples.
[A] disciple primarily refers to a dedicated follower of Jesus. This term is found in the New Testament only in the Gospels and Acts. In the ancient world, a disciple is a follower or adherent of a teacher. A disciple in the ancient biblical world actively imitated both the life and teaching of the master. It was a deliberate apprenticeship which made the fully formed disciple a living copy of the master.
The term "disciple" represents the Koine Greek word mathētḗs (μαθητής),3 which generally means "one who engages in learning through instruction from another, pupil, apprentice" 4 or in religious contexts such as the Bible, "one who is rather constantly associated with someone who has a pedagogical reputation or a particular set of views, disciple, adherent."
St. Paul frequently addresses the faithful as Brothers or Brethren.
The term brother occurs in verses like Acts 18:27. The King James Version renders the plural form used here as "brethren", while modern English versions have "brothers" (ESV) or "brothers and sisters" (NIV). The term comes from the theological concept of adoption, which says that believers are made part of God's family, and become his children.
1Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him, 2That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand. - 2 Thessalonians 2
We can se the the Scriptures of the New Testament as well as St. Paul employed different titles to the believers in Jesus Christ. He equally employed the term Saint(s) to those who followed The Way.
The Epistle to the Ephesians is written to the "saints at Ephesus" (Ephesians 1:1). In the New Testament the word is used to refer to Christians generally, but Robert S. Rayburn notes that "the name survived as a general title for Christians only through the second century." Rayburn suggests that the "juxtaposition of sainthood and martyrdom" in Revelation 17:6 may have resulted in the word becoming an "honorific title for confessors, martyrs and ascetics."
All believers, living and dead are a part of the Communion of Saints. The Catechism says, "We believe in the communion of all the faithful of Christ, those who are pilgrims on earth, the dead who are being purified, and the blessed in heaven, all together forming one Church; and we believe that in this communion, the merciful love of God and his saints is always [attentive] to our prayers" (CCC 962).
The saints are exemplars of how to follow Christ; they teach us how to live faithful and holy lives. The saints are our advocates and intercessors, and they are also friends and mentors.
The Saints in Scripture
In scripture, Paul addresses many of his letters to the various local communities under the title of “saints:” Romans, 1 and 2 Corinthians, Ephesians, etc. The term “saints” was also applied to those whom Christians served. In 1 Corinthians we read that Paul made a collection in Corinth for the relief of the saints in Jerusalem.
Paul also talks about the Communion of Saints in that each of us participates by baptism in the one Body of Christ. In his letter to the Romans, Paul tells us
“For as in one body we have many parts, and all the parts do not have the same function, so we, though many, are one body in Christ and individually parts of one another. Since we have gifts that differ according to the grace given to us” (Romans 12:4-6).
Paul is very clear that members of this common body had obligations to build up the community – these members were called “saints.” This is connected with the Jewish idea of being a holy nation, a covenanted people. The “saints” are those who have inherited the covenant. - Saints
There are many biblical saints named in the New Testament that are recognized as
Saints in the sense that both Catholics and Orthodox recognize them as being in heaven. St. Paul is obviously is using this title in a honorific sense in reference to all believers as those set apart from the rest of mankind. Does this mean that all believers were saved? Perhaps, but it could be called into question, especially when we read about what happened to Ananias and Sapphira in Acts 5:5-10
5 Now a man named Ananias, together with his wife Sapphira, also sold a piece of property. 2 With his wife’s full knowledge he kept back part of the money for himself, but brought the rest and put it at the apostles’ feet.
3 Then Peter said, “Ananias, how is it that Satan has so filled your heart that you have lied to the Holy Spirit and have kept for yourself some of the money you received for the land? 4 Didn’t it belong to you before it was sold? And after it was sold, wasn’t the money at your disposal? What made you think of doing such a thing? You have not lied just to human beings but to God.”
5 When Ananias heard this, he fell down and died. And great fear seized all who heard what had happened. 6 Then some young men came forward, wrapped up his body, and carried him out and buried him.
7 About three hours later his wife came in, not knowing what had happened. 8 Peter asked her, “Tell me, is this the price you and Ananias got for the land?”
“Yes,” she said, “that is the price.”
9 Peter said to her, “How could you conspire to test the Spirit of the Lord? Listen! The feet of the men who buried your husband are at the door, and they will carry you out also.”
10 At that moment she fell down at his feet and died. Then the young men came in and, finding her dead, carried her out and buried her beside her husband. 11 Great fear seized the whole church and all who heard about these events.
Although Ananias and Sapphira were possibly numbered amongst the saints of Jerusalem, they have never been venerated as saints by the Catholic Church in the sense of being honoured as saints in heaven.
Saints in the mind of St. Paul are those set apart and are worthy of being called saints. Even Strong’s term in Greek (ἅγιος) or hagios reaffirms this interpretation.
ἅγιος, , (from τό ἀγός religious awe, reverence; ἄζω, ἅζομαι, to venerate, revere, especially the gods, parents (Curtius, § 118)), rare in secular authors; very frequent in the sacred writings; in the Sept. for קָדושׁ;
- properly reverend, worthy of veneration: τό ὄνομα τοῦ Θεοῦ, Luke 1:49; God, on account of his incomparable majesty, Revelation 4:8 (Isaiah 6:3, etc.), equivalent to ἔνδοξος. Hence, used:
a. of things which on account of some connection with God possess a certain distinction and claim to reverence, as places sacred to God which are not to be profaned, Acts 7:33; τόπος ἅγιος the temple, Matthew 24:15 (on which passage see βδέλυγμα, c.); Acts 6:13; Acts 21:28; the holy land or Palestine, 2 Macc. 1:29 2Macc. 2:18; τό ἅγιον and τά ἅγια (Winer's Grammar, 177 (167)) the temple, Hebrews 9:1, 24 (cf. Bleek on Heb. vol. ii. 2, p. 477f); specifically that part of the temple or tabernacle which is called 'the holy place' (מִקְדָּשׁ, Ezekiel 37:28; Ezekiel 45:18), Hebrews 9:2 (here Rec.st reads ἅγια); ἅγια ἁγίων (Winer's Grammar, 246 (231), cf. Exodus 29:37; Exodus 30:10, etc.) the most hallowed portion of the temple, 'the holy of holies,' (Exodus 26:33 (cf. Josephus, Antiquities 3, 6, 4)), Hebrews 9:3, in reference to which the simple τά ἅγια is also used: Hebrews 9:8, 25; Hebrews 10:19; Hebrews 13:11; figuratively of heaven, Hebrews 8:2; Hebrews 9:8, 12; Hebrews 10:19; ἅγια πόλις Jerusalem, on account of the temple there, Matthew 4:5; Matthew 27:53; Revelation 11:2; Revelation 21:2; Revelation 22:19 (Isaiah 48:2; Nehemiah 11:1, 18 (Complutensian LXX), etc.); τό ὄρος τό ἅγιον, because Christ's transfiguration occurred there, 2 Peter 1:18; ἡ (Θεοῦ) ἅγια διαθήκη i. e. which is the more sacred because made by God himself, Luke 1:72; τό ἅγιον, that worshipful offspring of divine power, Luke 1:35; the blessing of the gospel, Matthew 7:6; ἁγιωτάτῃ πίστις, faith (quae creditur i. e. the object of faith) which came from God and is therefore to be heeded most sacredly, Jude 1:20; in the same sense ἅγια ἐντολή, 2 Peter 2:21; κλῆσις ἅγια, because it is the invitation of God and claims us as his, 2 Timothy 1:9; ἅγιαι γραφαί (τά βιβλία τά ἅγια, 1 Macc. 12:9), which came from God and contain his Words, Romans 1:2.
b. of persons whose services God employs; as for example, apostles, Ephesians 3:5; angels, 1 Thessalonians 3:13; Matthew 25:31 (Rec.); Revelation 14:10; Jude 1:14; prophets, Acts 3:21; Luke 1:70 (Wis. 11:1); (οἱ) ἅγιοι (τοῦ) Θεοῦ ἄνθρωποι, 2 Peter 1:21 (R G L Tr text); worthies of the O. T. accepted by God for their piety, Matthew 27:52; 1 Peter 3:5.
- set apart for God, to be, as it were, exclusively his; followed by a genitive or a dative: τῷ κυρίῳ, Luke 2:23; τοῦ Θεοῦ (equivalent to ἐκλεκτός τοῦ Θεοῦ) of Christ, Mark 1:24; Luke 4:34, and according to the true reading in John 6:69, cf. John 10:36; he is called also ὁ ἅγιος παῖς τοῦ Θεοῦ, Acts 4:30, and simply ὁ ἅγιος, 1 John 2:20. Just as the Israelites claimed for themselves the title οἱ ἅγιοι, because God selected them from the other nations to lead a life acceptable to him and rejoice in his favor and protection (Daniel 7:18, 22; 2 Esdr. 8:28), so this appellation is very often in the N. T. transferred to Christians, as those whom God has selected ἐκ τοῦ κόσμου (John 17:14, 16), that under the influence of the Holy Spirit they may be rendered, through holiness, partakers of salvation in the kingdom of God: 1 Peter 2:9 (Exodus 19:6), cf. Exodus 19:5; Acts 9:13, 32, 41; Acts 26:10; Romans 1:7; Romans 8:27; Romans 12:13; Romans 16:15; 1 Corinthians 6:1, 2; Philippians 4:21; Colossians 1:12; Hebrews 6:10; Jude 1:3; Revelation 5:8, etc.; (cf. B. D. American edition under the word).