Here we have one more instance where Joseph Smith, in his editing for the 1837 edition, removed a redundant subject pronoun. Such redundancy is quite common in the original text when the initial subject is followed by a long present participial clause (in this case, two conjoined ones). For further discussion, see under Mosiah 8:7; also see the list of examples under subject repetition in volume 3. The critical text will restore the redundant subject pronoun he in Alma 4:15 (“Alma having seen the afflictions of the humble followers of God … he began to be very sorrowful”).
Summary: Restore the redundant subject pronoun he in Alma 4:15 (“Alma … he began to be very sorrowful”).