v1-2 - Paul's familiar introduction that we've seen in other epistles.
v3-14 - It can be so easy to say to a person "I'm praying for you..." Paul goes a step beyond and tells the Colossians exactly why he's praying for them and what he's praying for:
WHY he's praying: to give thanks because he's heard about:
Their faith and love;
How they are bearing fruit as they grow in the gospel;
That God has rescued us from darkness and brought us into the kingdom of Christ, since we have redemption and forgiveness of sins in Him.
WHAT he's praying (continually) for:
That God will fill you with knowledge through the wisdom the Spirit gives;
...so that: you will live a live worthy of the Lord and will please Him in every way.
v15-23 - This passage is like a sidebar to the main passage reminding us once again who Jesus is and what He did.
Jesus is the image of God and the firstborn of creation, through whom all things have been made.
He has reconciled all things to Himself. In other words, He bought all that there is and paid with His blood which was shed on the cross.
Because you were bought by Christ, and the fullness of God dwells in Christ, you have been reconciled with God!
This is the Gospel message:
You are included in Christ. In Him, you've died to sin and have been raised to new life.
Therefore, He now presents you holy and blameless to the Father.
v24-20 - Paul has dedicated his life to preaching this gospel, and has endured significant suffering in doing so.