Continuing with Revelation 1:

1:8 I am Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty.

The first words of Jesus to John personally identify him with the "I AM' of Scripture, for He calls Himself the "Alpha and Omega." These are the first and last letters of the Greek alphabet. The title signifies, in the language of communication, the completeness with which God revealed Himself to mankind through Christ. This is nothing less than an official affirmation by Jesus of His personal deity. No ordinary human would ever say of himself, "I am the first and last."

We see here that God the Father, God the Word, and God the Holy Spirit are all three eternal. They each have no beginning and no end. Their Spirit is one. Their embodiments are three.