Life can be so busy, and we are so focused on the details surrounding us that we can often miss the important things that are in front of us.
Paul tells us to set our minds on things above (heavenly things) and not on the things of earth. God made the things here on earth for our enjoyment, but often, we let these things create a "curtain" between us and God rather than the window that allows us to see Him.
This is why Paul tells us to "put to death" our earthly desires. These things are what cause us to miss God’s glory. Paul is encouraging us to look more like God.