Adam Clarke on Psalms 149:7

To execute vengeance upon the heathen - This may refer simply to their purpose of defending themselves to the uttermost, should their enemies attack them while building their wall: and they had every reason to believe that God would be with them; and that, if their enemies did attack them, they should be able to inflict the severest punishment upon them.

Punishments upon the people - The unfaithful and treacherous Jews; for we find that some, even of their nobles, had joined with Sanballat and Tobiah; (see Neh 6:17-19): and it appears also that many of them had formed alliances with those heathens, which were contrary to the law; see Neh 13:15-29.