Ground yourself thoroughly in Scripture. In order to base your play on the Gospel, you need to know the Gospel.
Choose the theme for your script. You can base it on the life of one of the people in the New Testament or make it an illustration of a specific passage in the Bible.
Study other scripts to get a handle on characterization and plot development and how to integrate your theme into your script. Layon Gray began by checking out a book on playwriting from his library. You may need more training, such as a community theater class.
Decide if you want a contemporary setting, a historical setting or both. Historical settings are more respected, but require more research and cost more to produce. Contemporary settings are easier to write and allow for inserting references to current events.
Develop a compelling story. The Gospel message may be the greatest story ever told, but it needs to be told well.
Incorporate a strong comedy base, regardless of whether your script is comedy, tragedy or drama. Comedy lures the audience into a gospel play and provides a necessary release.
Revise the script according to feedback from the director and actors during rehearsal. Often, both will come up with better lines than were originally written.