In Colossians 1:15-17, the Apostle Paul wrote,

Colossians 1:15 Who is the image of the invisible God, the firstborn of every creature:
16 For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him:
17 And he is before all things, and by him all things consist.

These verses are speaking of Christ (v. 13) and tell us that He created all things because He existed "before all things," and that "all things consist" in Him. The gospel writer John clearly stated this same fact:

John 1:3 All things were made by him; and without him was not any thing made that was made.

He had to be pre-existent for this to be possible. He had to exist before anything was made since He created all things. The writer to the Hebrews said,

Hebrews 1:1 God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets,
2 Hath in these last days spoken unto us by his Son, whom he hath appointed heir of all things, by whom also he made the worlds;

I believe "worlds" here refers to the natural world and the spiritual world as opposed to "worlds" meaning other planets. Scripture, therefore, says that God created the natural world and the spiritual world by Him, telling us that before the created spirit world existed, the Son existed for it was by Him that it was created. Even Jesus Himself witnessed to His pre-existence, expressing in prayer to the Father concerning the glory He had with the Father "before the world was":

John 17:5 And now, O Father, glorify thou me with thine own self with the glory which I had with thee before the world was.
6 I have manifested thy name unto the men which thou gavest me out of the world: thine they were, and thou gavest them me; and they have kept thy word.

He prayed this because of what we are told in Philippians 2:5-11 that He hid His glory when He became flesh for the salvation of the world:

Philippians 2:5 Let this mind be in you, which was also in Christ Jesus:
6 Who, being in the form of God, thought it not robbery to be equal with God:
7 But made himself of no reputation, and took upon him the form of a servant, and was made in the likeness of men:
8 And being found in fashion as a man, he humbled himself, and became obedient unto death, even the death of the cross.

The Scriptures say Jesus was equal with God and that is because He was God the Son who was pre-existent. Because He did pre-exist, God could send His Son to be its Savior by His becoming flesh (John 3:16). As the pre-existent Son of God become flesh, He "MADE HIMESELF of no reputation, and TOOK UPON HIM the form of a servant, and WAS MADE IN the likeness of men." In order for these words to be true, Jesus had to pre-exist.