There is a connection between Exodus 20:4–5 and Colossians 1:15. The children of Israel were commanded to have no images to worship. An image eventually becomes an idol. Indeed, when God specifically commanded Moses to make an image (Numbers 21:8–9), it became an idol to them (2 Kings 18:4).
But God has specifically given us one Image to worship: Christ, who is the image of the invisible God.
In fact, when we consider John 3:14, we learn that the brass serpent was actually a type of the Son of Man lifted up. The children of Israel were committing idolatry when they worshiped the serpent that was lifted up for them, but God Himself invites us to worship the Son of Man who was lifted up for us. It is explicitly the Father's will that we should honor the Son as we honor the Father (John 5:23).
Isn't that cool? God knows we have a tendency to worship images, and He has given us an image to worship.