Rightly, therefore, the Lord again promises milk to the righteous, that the Word may be clearly shown to be both, "the Alpha and Omega, beginning and end; "
I am Alpha, and Omega. These, the first and last letters of the Greek alphabet, signify the same as what follows, the beginning, and the end, the first cause and last end of all intelligent beings, who is, and who was, and who is to come, the Almighty. These words agree only to him, who is the true God, and here are applied to our blessed Redeemer, who is to come and judge all. (Witham)
Alpha means beginning, and Omega means the end. Therefore he says, “I am the first and the last (Rev. 1:17).” He professes by the first that God has no beginning, and by the last that He has no end. But with there is nothing that is without beginning and end, he says this for us instead of saying, “without beginning nor end.” This is what God also said through Isaiah, “I, God, am first, and for the things coming, I Am.(Is. 41:4)”
the Almighty, and Lord of creation: He calls God Lord over the spiritual and visible creation.
Meanwhile, let this be my immediate answer to the argument which they adduce from the Revelation of John: "I am the Lord which is, and which was, and which is to come, the Almighty; "