And do not be conformed to this world, but be transformed by the renewing of your mind, so that you may prove what the will of God is, that which is good and acceptable and perfect. ~Romans 12:2
In the negative sense, ‘religion’ denotes the customs, mores, and traditions surrounding Christian faith empty of any actual relationship to or with God. This would include stuff like Christian merchandising, dressing up on Sunday, lighting candles, and so forth. These kinds of things are not the thing itself. They are not Christianity, and yet people often confuse these customs with the message about Jesus.
The message about Jesus, the gospel, is the core of Christianity, and it is not about any of these exterior, religious trappings. The gospel says we can be forgiven because of Christ’s substitutionary death on the cross. It says God will accept you because you call on Jesus in faith and not because of the way you act, dress, talk, or look. So in this sense, the gospel is almost irreligious. It abolishes typical concepts of religion…religion as a set of customs, mores, and traditions.