Why does the Bible refer to “the Alpha and the Omega?” What do these words or terms mean?
The Alpha is the first letter in the Greek alphabet and it’s where we get our word, “alphabet” from because the letters we use to construct words in our language are all contained in our alphabet. The phrase “alpha” can mean a beginning while the word “Omega” can mean the ending, but in Scripture it means much more than a beginning and an end. The Apostle John wrote of Jesus’ saying, “I am the Alpha and the Omega, the first and the last, the beginning and the end” (Rev 22:13) and writing about Jesus’ eternality, John wrote that Jesus said, “I am the Alpha and the Omega,” says the Lord God, “who is and who was and who is to come, the Almighty.” (Rev 1:8). That is, He was (as always having existed), He is (King of kings and Lord of lords), and is yet to come a second time (Rev 22:20). This is a description of God and is just as Isaiah the Prophet wrote of God, “Thus says the LORD, the King of Israel and his Redeemer, the LORD of hosts: “I am the first and I am the last; besides me there is no god” (Isaiah 44:6). Jesus told John “to the angel of the church in Smyrna write: ‘The words of the first and the last, who died and came to life’” (Rev 2:8), so this phrase also speaks of Jesus Who lived and died and yet lived again. Death could not hold Him because He was sinless, as the Apostle Peter wrote that “God raised him up, loosing the pangs of death, because it was not possible for him to be held by it” (Acts 2:24).
Since Jesus is God  and was with God in the beginning (John 1:1-2), He has always existed and there was never a time when Jesus did not exist, because by definition, God is eternal and has no beginning nor does He have an ending. Jesus’ body died but His spirit could not as at His death on the cross He cried out to God, “’Father, into your hands I commit my spirit!’ And having said this he breathed his last” (Luke 23:46). It was just after “Jesus had received the sour wine, he said, ‘It is finished,’ and he bowed his head and gave up his spirit” (John 19:3), so the spirit cannot die, even though Jesus’ earthly body did. His spirit went back to the Father Who received it, and today, He is at the right hand of the Father and is in all His glory. He was in the beginning and part of the beginning of creation, but He will also be at the end of this age when it will be said that “The world has now become the Kingdom of our Lord and of his Christ, and he will reign forever and ever” (Rev 11:15). For those who have trusted in Christ, death is not the end…it is just the beginning, and it is the time when we will be in the very presence of God (Rev 21:3; 22:4).
If you have a comprehensive encyclopedia or dictionary, and you started with the very first word in the alphabet, beginning with the letter “a,” and then move on to the very last letter of the alphabet, with the letter “z,” maybe you can understand why Jesus says that He is the Alpha and the Omega. What He is saying is that He’s everything from A to Z. If you took all human knowledge that has ever been known and that includes all words of knowledge, from A to Z, Jesus is everything in between and more. There is nothing that Jesus is not except sinful or having flaws. Jesus is the perfection that we need to enter the kingdom because it is only through Him that we can attain the very same righteousness as Jesus has and the same righteousness which God demands (2nd Cor 5:21). There are even some Christian hymns that sing that Jesus is “my everything” and He’s everything to me, and He should be considered as such because there isn’t anything that’s ever been made that was not made by Him (John 1:3), therefore, He is not only the Son of God but the King of kings and Lord of lords and all things, including the creation and us. He upholds everything by the word of His mouth and He rules over the universe and all that is in it. We must either acknowledge that or be in error.
Give God the glory and especially Jesus Christ. When you see Christ, either as your judge (Rev 20:12-15) or as your King (Rev 21:3; 22:4), then you will be like the Apostle John who wrote, “When I saw him, I fell at his feet as though dead. But he laid his right hand on me, saying, ‘Fear not, I am the first and the last, and the living one. I died, and behold I am alive forevermore, and I have the keys of Death and Hades’” (Rev 1:17-18). Clearly this is Jesus Who lived, died, and was alive again and will be “alive forevermore.” He holds the keys to death and hades (or the grave) because He has conquered the grave and brought victory from His death. By His death, we will never again be separated from God by our sins (Isaiah 59:2). It was “for this end Christ died and lived again, that he might be Lord both of the dead and of the living” (Rom 14:9) and He “died for us so that whether we are awake or asleep we might live with him” (1st Thess 5:10) and “since we believe that Jesus died and rose again, even so, through Jesus, God will bring with him those who have fallen asleep” (1st Thess 4:14). That includes all who have died in the faith and those who will be alive at His appearing; therefore He truly is the Alpha and the Omega.
Read more about Jesus here: 10 Interesting Bible Facts About Jesus 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), copyright © 2001 by Crossway, a publishing ministry of Good News Publishers. Used by permission. All rights reserved.