When Jesus began preaching, he began by calling people to repent and believe in the Good News of the Kingdom of God. Before Jesus, the prophets, including John the Baptist, called for repentance. Jesus gives the needed next step: Believe. It was not only necessary to turn away from sin, but then to commit to accept  and commit to all that God reveals as the path to salvation. In other words, it was the call to embrace the will of God as manifested in his revelations. As repentance is not a half-hearted act, so belief is not to be a pick and choose decision. It is a total all in for God. So often people want to be holy, which is the will of God, but not yet. The belief God expects of us can never be anything but "Yes", even though we may not fully understand. It is a surrender to God because he is God.