In Revelation 22:13, Jesus said, “”I am the Alpha and the Omega, the first and the last, the beginning and the end.” Revelation is filled with allusions to the Old Testament. Isaiah furnishes the background for Yahweh’s declaration that He is the “first and the last” (41:4; 44:6; 48:12). What is said of the Father is here affirmed of the Son, as He shares the divine essence. Consider the first part of the verse.

“I Am The Α

and The Ω.”  

What does this mean? Beale and McDonough observes:

These divine titles are figures of speech (merisms) in which the figurative point is to mention the opposite poles of something on order to emphasize the totality of all that lies between. The use of the first and last letters of the alphabet was typical of the ancients in expressing merisms. So the Jews could say that the law should be kept from aleph to tau. (Commentary on the NT Use of the OT, p.1055). 

The concept is that of totality, completeness. Interestingly, the blessings for obedience are listed in Leviticus 26:3-8, and begin with aleph (first letter of the Hebrew alphebet) and conclude with tau (last letter).

Wikipedia has some helpful info on merisms:

In rhetoric a merism is the combination of two contrasting words, to refer to an entirety. For example, when we mean to say that someone searched thoroughly, everywhere, we often say that someone “searched high and low”. You also say “ladies and gentlemen” and the “young and old”.

Merisms also figure in a number of familiar English expressions. The phrase lock, stock, and barrel originally referred to the parts of a gun, by counting off several of its more conspicuous parts; it has come to refer to the whole of anything that has constituent parts. Basically, and everything in between – all encompassing.

In biology, a merism is a repetition of similar parts in the structure of an organism (Bateson 1894). Such features are called meristic characters, and the study of such characters is called meristics.

Merisms are conspicuous features of Biblical poetry. For example, in Genesis 1:1, when God creates “the heavens and the earth” (KJV), the two parts combine to indicate that God created the whole universe. Similarly, in Psalm 139, the psalmist declares that God knows “my downsitting and mine uprising”, indicating that God knows all the psalmist’s actions. 

Greek Letters Alpha and Omega. commons.wikipedia.org

Alpha is the first letter in the Greek alphabet; omega is the last. We would say, “Everything from A to Z. What is affirmed is that everything is summed up in Jesus. He is the beginning of creation, responsible for its origin. He is the end, and will bring it to a conclusion. He is what all history is about from beginning to end. Contextually in Revelation, it was not ultimately the Roman Emperors who ruled, but rather Jesus is KING OF KINGS AND LORD OF LORDS (Rev.19:16).

Romans 11:36: “For from Him and through Him and to Him are all things. To Him be the glory forever. Amen.”

Ephesians 1:9-10: “He made known to us the mystery of His will, according to His kind intention which He purposed in Him with a view to an administration suitable to the fullness of the times, that is, the summing up of all things in Christ, things in the heavens and things on the earth.”

Col. 1:15-20: 

15 He is the image of the invisible God, the firstborn of all creation. 16 For by Him all things were created, both in the heavens and on earth, visible and invisible, whether thrones or dominions or rulers or authorities– all things have been created through Him and for Him. 17 He is before all things, and in Him all things hold together. 18 He is also head of the body, the church; and He is the beginning, the firstborn from the dead, so that He Himself will come to have first place in everything. 19 For it was the Father’s good pleasure for all the fullness to dwell in Him, 20 and through Him to reconcile all things to Himself, having made peace through the blood of His cross; through Him, I say, whether things on earth or things in heaven.

What is meant by Jesus’ being the Alpha and Omega? He is Everything! Observe:

1. Jesus’ absolute Deity is affirmed.

2. He is Creator.

3. He is Redeemer.

4. He is Sovereign Ruler over all.

5. He is Judge.

“I have found a friend in Jesus,

He’s everything to me,

He’s the fairest of ten thousand to my soul;

He’s the Lily of the Valley, in Him Alone I see

All I need to cleanse and make me fully whole. “