The role of the prophet is only to bring Israel back to the Tora (i.e. mitsva observance); which is the same as saying back to holiness and communion with God.
Let me succinctly illustrate this 'trinity' of God, holiness, and mitsva observance.
The only way sinful man can commune with a holy God is through [moral] standards and [ritual] practices that were given to us by the Creator Himself; like when He says "Be holy, as I am holy" (Lev.20:26).
And -- of course -- the way to this 'holiness' is through observance of the mitsvahs.