This is an unusual yet informative response. The Lord says, “Don’t worry about it.” “What they do doesn’t concern you, for you have been faithful.” The Lord’s answer hints that indeed the Gentiles will lack that grace for which Moroni prays. Certainly, if the grace of the Gentiles is to be judged by how they have received the Book of Mormon, then they are certainly deficient.
Hugh Nibley
“In reply to his request, the Lord gave Moroni no firm promise. His only answer was: ’If they have not charity it mattereth not unto thee, thou hast been faithful’ (Ether 12:37). God will not force any man to have charity—that would not be charity, which must be spontaneous and unsolicited, as Paul says, seeking nothing for itself (1 Corinthians 13:5). Charity is the one thing a person must have in himself and of himself. And so there Moroni leaves it: will we have charity, or will we not?” (The Prophetic Book of Mormon, p. 467)