The Bible or Tradition, page-48

It was from this date of Pentecost 33 CE that they became baptized Christian disciples of Jesus Christ

It’s really irrelevant when Christian first became / or first called Christians, Eph 3:1-10 tells us that it was God’s plan from the very foundation, baptism is just a process form which all mankind Jews and Gentiles, including you and me can enter into God’s kingdom made manifest first through Christ then through the Church.

Here MrG, along with other bible verse is why the church is very important for salvation and that it cannot go into apostacy as this mystery or God’s plan has moved from Christ to the church, and that is the very same church founded by himself as seen in the bible, not any one that comes along 1500-2000 years later and pretend they are it.

Read the whole chapter to see exactly what it’s says, there is a big difference from assuming what the bible says then taking a snippet from here and there pasting them together to form an out of contexts point to justify one's view.

Eph 3: 1 With this in mind, I fall on my knees; I, Paul, of whom Jesus Christ has made a prisoner for the love of you Gentiles.[1] 2 You will have been told how God planned to give me a special grace for preaching to you; 3 how a revelation taught me the secret I have been setting out briefly here;[2] 4 briefly, yet so as to let you see how well I have mastered this secret of Christ’s. 5 It was never made known to any human being in past ages, as it has now been revealed by the Spirit to his holy apostles and prophets, and it is this: 6 that through the gospel preaching the Gentiles are to win the same inheritance, to be made part of the same body, to share the same divine promise, in Christ Jesus. 7 With what grace God gives me (and he gives it in all the effectiveness of his power), I am a minister of that gospel; 8 on me, least as I am of all the saints, he has bestowed this privilege, of making known to the Gentiles the unfathomable riches of Christ, 9 of publishing to the world the plan of this mystery, kept hidden from the beginning of time in the all-creating mind of God. 10 The principalities and powers of heaven are to see, now, made manifest in the Church,