Christ is the visible image of the invisible God. He existed before God made anything at all and is supreme over all creation.
References for Colossians 1:15
Christ is the one through whom God created everything in heaven and earth. He made the things we can see and the things we can't see -- kings, kingdoms, rulers, and authorities. Everything has been created through him and for him.
He existed before everything else began, and he holds all creation together.
Christ is the head of the church, which is his body. He is the first of all who will rise from the dead, so he is first in everything.
References for Colossians 1:18
For God in all his fullness was pleased to live in Christ,
and by him God reconciled everything to himself. He made peace with everything in heaven and on earth by means of his blood on the cross.
This includes you who were once so far away from God. You were his enemies, separated from him by your evil thoughts and actions,
yet now he has brought you back as his friends. He has done this through his death on the cross in his own human body. As a result, he has brought you into the very presence of God, and you are holy and blameless as you stand before him without a single fault.
But you must continue to believe this truth and stand in it firmly. Don't drift away from the assurance you received when you heard the Good News. The Good News has been preached all over the world, and I, Paul, have been appointed by God to proclaim it.