The Book of Colossians is Paul's letter to the Christians at Colosse. Paul had not visited Colosse. But he often prayed for the Christians there (Colossians 1:3-14).
Paul reminded the Christians about the importance of Jesus. Jesus is God, and he created everything. Then, Jesus became a man, so that he could die for us. Because Jesus died, God will forgive us. If we invite Jesus into our lives, we will become friends of God (Colossians 1:15-23).
Then, Paul warned the Christians about some people (Colossians 2). These people wanted the Christians to obey the ancient rules of the Hebrew nation. And these people said that real Christians must obey all such rules. Paul did not agree. He wrote that these rules were human traditions (Colossians 2:8). Christians ought to obey Christ, instead of tradition. Traditions might seem wise, but they cannot help us to live good lives (Colossians 2:23).
Paul reminded the Christians how they should live. They should think about the things in heaven (Colossians 3:2), because they belong with Christ (Colossians 3:3-4). They should not do evil deeds (Colossians 3:5-11). Instead, they should love other people (Colossians 3:12-14). And they should serve God (Colossians 3:15-17).