Mormon did not regain faith in his people. He no longer believed, though perhaps he hoped, that they would repent and return to the Lord. Nevertheless, in spite of what he saw as a hopeless situation, he allowed the people to convince him to return as the head of the armies. The conditions that had caused him to leave that position had not changed, but Mormon perhaps saw that they needed what hope they could muster. He returned.
The first mentioned action in which he led the armies was as the Nephites fled to the city of Jordan. There they were able to hold off the Lamanite advance and earn some respite.