“So they went out and preached that people should repent” (Mark 6:12).
Federal Visionists love this verse because they think that Jesus sent his twelve disciples out to preach the gospel. While a common misconception, this is an utter departure from the Reformers.
The Reformed faith has always insisted that the heart of the gospel is justification, which is received by faith alone. Repentance is a post-justification work of sanctification. It has nothing to do with justification, and therefore, nothing to do with the gospel.
Thus, when Jesus commissioned his disciples to preach that people should repent, he was sending them out to preach the message of sanctification, not the gospel.