Jesus clarified the gospel against the Pharisees and the Anti-Roman agitators of his day. Paul clarified the gospel against the Judaizers in the church. The Protestant Reformers clarified the gospel against the Catholic Church of the 15th century.
The gospel must be clarified against the unique competitor idea that arises in each generation to compete with it. If you teach and preach the gospel only as it was clarified against a competing idea of a past generation, your preaching will be sufficient to save but not be fully effective to disciple.