Jamieson, Fausset and Brown on Isaiah 58:6

6. loose ... bands of wickedness--that is, to dissolve every tie wherewith one has unjustly bound his fellow men (Le 25:49, &c.). Servitude, a fraudulent contract, &c.

undo ... heavy burdens--Hebrew, "loose the bands of the yoke."

oppressed--literally, "the broken." The expression, "to let go free," implies that those "broken" with the yoke of slavery, are meant (Ne 5:10-12; Jr 34:9-11, 14, 16). Jerome interprets it, broken with poverty; bankrupt.