Albert Barnes on Revelation 22:13

I am Alpha and Omega, etc. Rev 1:8,11. The idea here is, that he will thus show that he is the first and the and last --the beginning and the end. He originated the whole plan of salvation, he will determine its close; he formed the world, and he will wind up its affairs. In the beginning, the continuance, and the end, he will be recognised as the same being presiding over and controlling all.

(e) "Alpha and Omega" Isa 44:6