SummaryJesus' preexistence means that he existed before he came...

https://www.blueletterbible.org/faq/don_stewart/don_stewart_210.cfm

The doctrine of Jesus' preexistence means that he existed before he came to earth as a human being. There are a number of passages that make this clear.

The Word Became Flesh

This key New Testament verse says God became a human being in Jesus.

And the word became flesh and dwelt among us, and we beheld his glory, the glory as of the only begotten of the Father, full of grace and truth (John 1:14).

Jesus Is At The Father's Side

John says Jesus at the Father's side

No one has ever seen God, but God the one and only, who is at the Father's side, has made him known (John 1:18).

Jesus Existed Before Abraham

Jesus said that he existed before Abraham.

Jesus said to them, "Most assuredly, I say to you, before Abraham was, I AM" (John 8:58).

Jesus Is Preeminent Over All Creation

Paul also said that Jesus was preeminent over all creation.

He is the image of the invisible God, the firstborn over all creation (Colossians 1:15).

Jesus Had Past Glory

While here on earth, Jesus himself spoke about his past glory.

And now, Father, glorify me in your presence with the glory I had with you before the world began (John 17:5).

Jesus also said.

Father, I desire that they also whom you gave me may be with me where I am, that they may behold my glory which you have given me; for you loved me before the foundation of the world (John 17:24).

We do not exactly know what this glory consisted of.

Jesus Took The Form Of A Servant

Paul wrote about the coming of Jesus to the earth as taking the form of a servant.

Who, being in very nature God, did not consider equality with God something to be grasped, but made himself nothing, taking the very nature of a servant, being made in human likeness (Philippians 2:6,7).

Summary

Jesus' preexistence means that he existed before he came to earth. The Bible speaks of Jesus being at the side of the Father. His position was of one who was preeminent over all creation. Scripture also speaks of his previous glory. He laid aside that glory when he came to earth as a human.