Here is another typo by the typesetter for the 1841 British edition; this error has persisted in the LDS text. The intrusive a before repentance was probably influenced by the preceding a’s in “a law given and a punishment affixed”. In other places in the text where we get repentance occurring with the verb grant, there is no determiner for the noun repentance:
In fact, the indefinite article a never occurs as the determiner for repentance in the original text. Elsewhere repentance occurs as a noncount noun. It usually takes no determiner at all (as originally here in Alma 42:22 and 87 other times in the text). There are cases where repentance takes a determiner, but it is never a:
their 5 times
your 3 times
the 2 times
no 1 time
And since repentance is noncount, it never occurs in the plural (as repentances). Thus the occurrence of “a repentance” in the current LDS text for Alma 42:22 is textually unacceptable.
Summary: Restore in Alma 42:22 the original text without any determiner for repentance; the word repentance consistently functions as a noncount noun in the text; thus the intrusive a before repentance in the LDS text creates an exception.