In Doctrine and Covenants, section 18, dated June 1829, the Lord not only mentioned the apostolic calling of Oliver Cowdery and David Whitmer but also commanded them and "all men everywhere" (D&C 18:9) to repent and come unto him, for they could be saved only through him.
9. And now, Oliver Cowdery, I speak unto you, and also unto David Whitmer, by the way of commandment; for, behold, I command all men everywhere to repent, and I speak unto you, even as unto Paul mine apostle, for you are called even with that same calling with which he was called.
11. For, behold, the Lord your Redeemer suffered death in the flesh; wherefore he suffered the pain of all men, that all men might repent and come unto him.
12. And he hath risen again from the dead, that he might bring all men unto him, on conditions of repentance.
13. And how great is his joy in the soul that repenteth!
21. Take upon you the name of Christ, and speak the truth in soberness.
22. And as many as repent and are baptized in my name, which is Jesus Christ, and endure to the end, the same shall be saved.
25. Wherefore, if they know not the name by which they are called, they cannot have place in the kingdom of my Father.
These few lines I write unto you feeling anxious for your steadfastness in the great cause of which you have been called to advocate and also feeling it a duty to write to you at every opportunity[.] remember the worth of Souls is great in the Sight of God[.] behold the Lord your God Suffered death upon the cross after the manner of the flesh. wherefore he Suffered the pains of all men that all men might repent and come unto him and he and he [sic] hath risen again from the dead that they might bring all men unto him upon conditions of repentance and how great is his joy in the Soul that repents and behold he commandeth all men everywhere to repent and not only be baptized and not only men but women [and] children which have arrived to the years of accountability. Stir up the minds of our friends against the time we come unto you that thus [then?] they may be willing to take upon them the name of Christ for that is the name by which they shall be called at the last day and if we know not the name by which we are called I fear we shall be found on the [left?] hand. I have many things to write but if the Lord will I shall shortly come unto you then tell Mrs. [Mr.?] Rockwell that those shoes fit well and I received them as from the Lord[.] I tell him that what ever he does in the cause of Zion he will in no wise loose his reward.