"Therefore do not let anyone judge you by what you eat or drink, or with regard to a religious festival, a New Moon celebration or a Sabbath day. These are a shadow of the things that were to come; the reality, however, is found in Christ." (NIV)
Christianity is not a religion. That may sound strange to many, but it is still very true. Many religions have been built around Christianity, but religion is merely a set of rituals or rules that express faith in a particular belief system. Christianity (in this case) is that belief system.
In Colossians Paul warns about conflicts between Christians whose religions differ. At the time, he was probably more concerned with those who observed the Jewish rites and those who did not. Judaism was built on the law of God after all, so many Jews had difficulty moving from living under the law to living under God's grace. They had been God's only chosen people for so long, and now the doors of Heaven had been opened to Gentiles as well. "Or is God the God of Jews only? is he not the God of Gentiles also? Yea, of Gentiles also:" (Romans 3:29 ASV)
Paul says that we should not be judged by religion. The Jewish tradition of the day was "a shadow of the things that were to come," fulfilled by Christ's life, death and resurrection. What is important to a Christian should not be rituals or rites, but faith in God and acceptance of the grace He provided to us through Jesus' death on the cross.
The same is true of the varying sects and denominations within the church today. Those who worship with a pipe organ and those who do so with electric guitars are all still worshipping the same God. We are all part of the same Body of Christ, so long as we hold true to certain basics of our faith, "so we, who are many, are one body in Christ, and severally members one of another." (Romans 12:5 ASV) We often bicker among ourselves saying one church is too legalistic, another is too charismatic, but in reality it's like the eyes of the body chastizing the hands for not being able to see and the tongue being angry with the ears because they refuse to speak. If we can't even love each other, how can we ever hope to reach out to the rest of the world?