The loss of the preposition of before Isaac in the 1837 edition is probably a typo since elsewhere that edition (and others) have maintained the repetitive elements in conjuncts involving the names Abraham, Isaac, and Jacob. The 1908 RLDS edition restored the repetitive of before Isaac, probably by reference to the printer’s manuscript rather than the 1830 edition. The original conjunctive phraseology in Mosiah 23:23 is also found in Acts 3:13 (the King James version). For some discussion regarding the repetition of elements in this particular conjunctive expression, see under 1 Nephi 19:10. Also see the general discussion under conjunctive repetition in volume 3. The critical text will, of course, restore the repeated of here in Mosiah 23:23.
Summary: Restore in Mosiah 23:23 the repeated preposition of before Isaac (“the God of Abraham and of Isaac and of Jacob”), the reading of the earliest textual sources.