Hopefully Becks “message” of returning to God was indeed taken with the idea of Christian roots.....but those who know Mormonism recognize that Mormonism does not have it's roots in the Christian Christ....rather an impostor.
I believe that a "sincere" belief in Christ necessitates repentence. This is what Paul means he says you must accept him in your "heart". But your point is still well taken, repentence should be mentioned specifically when explaining the Gospel. Jesus' first sermon after being baptized was "repent and believe in the gospel."