Here the 1830 typesetter dropped a small word, the definite article the. Although the original manuscript is not extant here, there is clearly room between the surviving fragments for a the. Elsewhere in the text, there are examples where diligence is preceded by various kinds of determiners, including none at all (listed as null here):
all diligence 12
null diligence 6
the diligence 5
their diligence 4
your diligence 2
his diligence 1
thy diligence 1
so much diligence 1
In this particular case of Alma 28:14, we actually expect the definite article the because diligence has a postmodifier (namely, “of men to labor in the vineyards of the Lord”). A similar example is found earlier in the text:
In this second case, diligence and heed is postmodified by the relative clause “which ye have given unto my word”. Thus the definite article is expected.
One might also ask here if the preposition of that follows call in Alma 28:14 is in fact correct. The original manuscript is not extant for this word. One possible emendation would be to replace of with for, which would undoubtedly alleviate the awkwardness of this passage:
The for could fit in the lacuna of 𝓞. On the other hand, there is independent evidence for the selection of the preposition of since later on in this verse we have one more example of great followed by a noun; and there we get the preposition of just as before (in fact, the of is conjunctively repeated):
Summary: Restore the definite article the before diligence in Alma 28:14 (“the great call of the diligence of men to labor in the vineyards of the Lord”); also retain the preposition of after call since it is consistent with the use of of in a similar expression later in the verse.