Revelation 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.

Alpha and Omega; these are the first and last letters of the Greek alphabet. By applying them to Himself, Jesus Christ shows that He is the cause and end of all things. Compare  Isa 44:6 Thus saith the LORD the King of Israel, and His Redeemer the LORD of hosts; I am the first, and I am the last; and beside Me there is no God.

By applying this title Alpha and Omega along with the phrase, Is–was–is to come to The Lord Jesus Christ, we find more proof of the self-existent, unchangeable, eternal nature of The Lord Jesus.

Any teaching that diminishes the deity of Jesus Christ is antichrist.

Re 21:6 And he said unto me, It is done. I am Alpha and Omega, the beginning and the end. I will give unto him that is athirst of the fountain of the water of life freely.

This is clearly a reference to The Father, which once again proves that Jesus and The Father are one in nature and in essence. But this is also a call to salvation. If you are tired of life, tired of living after the things of this world, tired of a dead religious system, God invites you to take of the water of life freely. Repent of your sin, enter into sweet fellowship with God. Come and drink from Christ, Who is fountain of the water of life freely.