A good Christian song can be secular or non-secular. Secular Christian music will have a strong religious foundation. The lyrics will typically be distinctly religious and coming from a specific religious background. Secular songwriting is good if you are writing songs strictly for a church or religious audience, but if you want to reach a wider audience with the message of your songs, consider writing non-secular music. This doesn't mean the music can't be about God or worship. Non-secular music is spiritual without focusing on one religion and without overworking the religious element.
Writing Christian songs is a lot like writing any type of song. Use the same basic elements of rhythm and melody combined with lyrics to present a message or story in song. To reach the widest possible audience with your songs, consider lyrics that can be interpreted with a dual meaning. A song about your deep feelings for Christ can be written without ever mentioning the name of Christ. This makes your lyrics more open to interpretation to a mainstream audience, yet the meaning of the lyrics still hold the religious or spiritual meaning for your core audience. There are no rules about writing lyrics for Christian songs, but the way you go about it will determine your success outside the realm of listeners who enjoy Christian music. The goal of a good Christian song is to deliver a positive, inspirational message of hope that can be understood by as many listeners as possible. These are universal messages that know no religious bounds.
Music for most popular Christian songs uses the same chords and notes as other songs. When you write Christian songs, think in terms of big, sweeping sound. Think about writing in major keys and using techniques such as key changes going into verses. Moving up an entire step at the end of a song can provide an uplifting spiritual sound to build the song finale upon. Add parts for a choir or old-time gospel stylings to your contemporary composition, which can help produce a memorable piece.