[BenghaziMemoriam]

"...if we turn our attention to the beginnings of Apostolical teaching after His ascension, we shall find ourselves unable to fix an historical point at which the growth of doctrine ceased, and the rule of faith was once for all settled. Not on the day of Pentecost, for St. Peter had still to learn at Joppa that he was to baptize Cornelius; not at Joppa and Cæsarea, for St. Paul had to write his Epistles; not on the death of the last Apostle, for St. Ignatius had to establish the doctrine of Episcopacy; not then, nor for centuries after, for the Canon of the New Testament was still undetermined. Not in the Creed, which is no collection of definitions, but a summary of certain credenda, an incomplete summary, and, like the Lord's Prayer or the Decalogue, a mere sample of divine truths, especially of the more elementary. No one doctrine can be named which starts complete at first, and gains nothing afterwards from the investigations of faith and the attacks of heresy."
- John Henry Newman, Development of Christian Doctrine

"Now, as you know, it has been held from the first, and defined from an early age, that Mary is the Mother of God. She is not merely the Mother of our Lord's manhood, or of our Lord's body, but she is to be considered the Mother of the Word Himself, the Word incarnate. God, in the person of the Word, the Second Person of the All-glorious Trinity, humbled Himself to become her Son."
- John Henry Newman, Discourses to Mixed Congregations

[kosciusko51]

If your point is true that not all Christian teachings were not completed with the apostles, how could the first century believer know what was necessary for salvation? Or did they have sufficient information at that time?

And why should any current Christian be held accountable for beliefs the early Christians were not taught by the apostles?