The Heart of Man

Helaman 13:3; “But behold, the voice of the Lord came unto him, that he should return again, and prophesy unto the people whatsoever things should come into his heart.”

Jeremiah 17:9; “The heart is deceitful above all things, and desperately wicked: who can know it?”

Why would God tell a prophet to prophesy what is in his heart when God had already stated through Jeremiah the heart of man is wicked 600 years prior? The prophecy wouldn’t be from God, it’d be from “Samuel the Lamanite” if there was such a person.