Revelation 1:8

Greek, "I am the Alpha and the Omega." The first and last letters of the alphabet. God in Christ comprises all that goes between, as well as the first and last. the beginning and the ending--omitted in the oldest manuscripts, though found in Vulgate and Coptic. Transcribers probably inserted the clause from Rev 21:6. In Christ, Genesis, the Alpha of the Old Testament, and Revelation, the Omega of the New Testament, meet together: the last book presenting to us man and God reconciled in Paradise, as the first book presented man at the beginning innocent and in God's favor in Paradise. Accomplishing finally what I begin. Always the same; before the dragon, the beast, false prophet, and all foes. An anticipatory consolation to the saints under the coming trials of the Church. the Lord--The oldest manuscripts read "the Lord God." Almighty--Hebrew, "Shaddai," and "Jehovah Sabaoth," that is, "of hosts"; commanding all the hosts or powers in heaven and earth, so able to overcome all His Church's foes. It occurs often in Revelation, but nowhere else in the New Testament save Co2 6:18, a quotation from Isaiah.

— Jamieson-Fausset-Brown Commentary (public domain)