If you share the Gospel (especially if you talk to Mormons or Jehovah's Witnesses), you will see that this is a highly practical study and one that was very important for me three times in the past week alone – one time for which I was unprepared. You will see that the early church already had a firm believe in the Deity of Christ, but only had to formally write it out after heresies kept sprouting up.Timeline:
The Gospel of John was written in 80-90 AD and it is the Gospel which asserts the Deity of Christ most fully (cf. John 1:1, John 10:30-35, John 20:28, etc.)
Polycarp (A.D. 69-155), bishop of Smyrna, was a disciple of the apostle John. He wrote, "Now may the God and Father of our Lord Jesus Christ, and the eternal High Priest Himself, the (Son of) God Jesus Christ, build you up in faith . . ."
Ignatius of Antioch (he died around A.D. 107) spoke often of "our God, Jesus Christ." He also wrote letters to Polycarp asserting the same thing.
Justin Martyr (110-166 A.D.) "Our Christ conversed with Moses under the appearance of fire from a bush." It was not the Father of the universe who thus spoke to Moses; but ' 'Jesus the Christ, ' ' ' 'the Angel and Apostle," " who is also God," yea the God of Abraham, Isaac, and Jacob," and "the I am that I am'' (First Apology, lxii; lxiii).