To do this I used Romans 3:21-26. The Colossians were a "Romans" people. What I mean by that is that Roman's 3:21-26 establishes both who people were before Christ and who they are now. This passage in Romans in a nutshell defines God's people. They used to be this and now they are that. Not only that, but it establishes the inclusion of the Gentiles in to the covenant of God. I'm not sure that this passage is the best "introduction" to Colossians, but it seemed good at the time an continues to seem to hold up as I have preached three weeks into Colossians.