D&C 6

The Lord said to Joseph Smith and Oliver Cowdery -

"Say nothing but repentance unto this generation..."  (Doctrine and Covenants | Section 6:9)

Only considering this one sentence, one might assume that all we do is call people to repentance, but the Lord adds -

"...keep my commandments, and assist to bring forth my work, according to my commandments, and you shall be blessed."  (Doctrine and Covenants | Section 6:9)

Obviously one cannot repent unless they are taught the commandments and establish faith in Jesus Christ.  President Boyd K. Packer taught -

“True doctrine, understood, changes attitudes and behavior. The study of the doctrines of the gospel will improve behavior quicker than a study of behavior will improve behavior."

Thus an essential need to say repentance if the need to first teach truth, doctrine, principles, and the commandments is all part of "saying repentance".  One would do best to watch and learn from those we sustain, the prophets, seers, and revelators.