ขอขมา is to ask pardon. The chant is a single stanza said three times with only its object changed — the Buddha, then the Dhamma, then the Sangha — which is the same shape as several of the salutations earlier in the book.

What is asked for is narrower than it may appear. This tradition has no mechanism by which a fault is cancelled because it has been confessed, and the chant does not ask for one. What the formula does is bring a fault into the open and make a statement about the future.

Each stanza has four movements. First the three doors through which anything at all is done — กาเยนะ วาจายะ วะ เจตะสา วา, by body, by speech, or by mind. Then the fault. Then the request that it be accepted. Then the reason for asking, which is the line that carries the weight.

That reason is กาลันตะเร สังวะริตุง — that in time to come I may be restrained. The pardon is asked for the sake of future restraint, not for relief from the past, and nothing in the chant asks for anything to be undone. What is sought is permission to go on rather than absolution for having stumbled.

Its use follows from that. Someone about to begin something — a retreat, a residence, a day of precepts — starts by naming what has gone wrong instead of carrying it unspoken. The chant is short because its work is only to get the thing said.