The question here is whether the compound subject should be treated as singular or plural. The original text has the singular verb is for the subject “his faith and hope”. In the 1874 RLDS edition, the singular verb form is was changed to are. The 1908 RLDS edition restored the original is, but in the 1953 RLDS edition the secondary plural are was once more adopted. There are several other places where the 1953 RLDS edition emended the grammatical number for compound subjects that can be interpreted as either singular or plural, namely, in Jacob 7:23, Helaman 3:32 (two times), and Helaman 11:15.
For Moroni 7:44 there is definite evidence that “faith and hope” should be considered a unit. First of all, the his is not repeated in the conjunctive phrase; we do not have “his faith and his hope”, which would argue that we have two separate conjuncts. Moreover, in the famous King James passage in 1 Corinthians 13:13, the conjoined “faith hope charity” is grammatically treated as a singular: “and now abideth faith hope charity / these three”. One could argue that the third person singular -eth ending shows that faith, hope, and charity are being considered as a unit. Another possibility, pointed out by Don Brugger (personal communication) is that the singular verb form could show that each of the three nouns in the series is being considered individually, as if abideth is ellipted from before each of the last two nouns. In this case, however, the King James translators were probably literalistically following the Greek original, where the verb is the singular menei because the three nouns are all abstract. (This use of the singular abideth actually dates back to William Tyndale’s 1526 translation of the New Testament.) For discussion of the use in New Testament Greek of singular verb forms with abstract nouns and pronouns in the plural, see section 133 in F. Blass and A. Debrunner, A Greek Grammar of the New Testament and Other Early Christian Literature, edited by Robert W. Funk (Chicago, Illinois: The University of Chicago Press, 1961), 173–174.
This same grammatical singular verb form is used in a similar expression in the Book of Mormon text: “faith hope and charity bringeth unto me” (Ether 12:28). In that case, however, one could interpret the -eth form as an example of the tendency in the Book of Mormon text to use the -(e)th ending with plural subjects as well as singular ones (see the discussion under the 1 Nephi preface for the clause “Nephi’s brethren rebelleth against him”).
Interestingly, the original text for a revelation given to Joseph Smith in February 1829 had the third person singular verb form qualifies for the subject “faith hope charity and love”:
The first edition of the Doctrine and Covenants (in 1835) also had qualifies (found there under section 31). But this form was later edited to qualify, so that modern editions read with the plural verb form (now section 4 in the LDS Doctrine and Covenants). For the most part, the -es ending is restricted to third person singular usage in the original Book of Mormon text, which suggests that “faith hope charity and love” in this early revelation, given during the general time period when Joseph Smith was translating the Book of Mormon, is being considered as a unit.
Given that both Ether 12:28 and 1 Corinthians 13:13 (in the King James Bible) treat “faith hope (and) charity” as a unit, the singular is in “his faith and hope is vain” should also be retained in Moroni 7:44 in the standard text. The critical text will, of course, retain the earliest reading with the singular is.
Summary: Retain the singular verb form is in Moroni 7:44 as well as the singular bringeth in Ether 12:28; the singular verb usage with conjunctive phrases involving faith, hope, and charity appears to be intended, just as it is in 1 Corinthians 13:13.