The 1837 edition omitted the definite article the before rock, probably unintentionally. In his editing for the 1837 edition, Joseph Smith did not mark this deletion in the printer’s manuscript. And there is clearly nothing inappropriate about the original reading with its repetition of the definite article the. The critical text will restore the repeated the in this expression.
The original Book of Mormon text has many examples of the repeated determiner in conjunctive constructions. Here in Jacob 7:25 we have a conjoining of God and rock. There are two other examples that conjoin these two nouns, and in each case we have a determiner for both conjuncts:
For further discussion of the Book of Mormon tendency to repeat the determiner in conjoined noun phrases, see conjunctive repetition in volume 3.
Summary: In accord with the reading of the earliest textual sources, restore the definite article the before rock in Jacob 7:25.