George Leo Haydock, on Ps 136:4

“How shall we sing the song of the Lord in a strange land?”

“Land. They were oppressed with grief, (Ecclesiasticus xxii. 6.) and unwilling to expose sacred things to profanation, though there was no prohibition for them to sing out of Judea, for their mutual comfort. (Calmet) — They excuse themselves on both accounts.”

Imported from an open dataset — not yet checked against the printed edition.