Final answer:
The main idea of the social gospel movement was social justice through Christianity. It sought to apply Christian principles to address major social problems such as poverty, crime, and child labor.
Step-by-step explanation:
The main idea of the social gospel movement was social justice through Christianity. This movement emerged during the early twentieth century and sought to apply Christian principles to address major social problems such as poverty, crime, and child labor. Adherents of the movement were inspired by the question 'What would Jesus do?' and believed in the obligation to serve the poor and work towards a more just society. The social gospel movement also motivated campaigns for fair treatment of workers and challenged discriminatory practices.