What does Psalm 129:4 mean?

It may seem strange that Scripture so often refers to God as loyally loving and merciful (Exodus 15:13; Psalms 36:5; 86:15; 118:1). Israel's history of persecution was nearly constant; likened to how a plow makes long cuts in a field, with only tiny breaks in between each path of destruction (Psalm 129:3). Despite this, attempts to imprison or destroy Israel have ultimately been thwarted. The nation survived because of God's influence.

Cords are associated with imprisonment (2 Samuel 22:6; Psalms 18:4–5; 119:61). That God cut the cords of the wicked evokes His work in freeing Israel from their various captors (Exodus 12:41; Jeremiah 29:10; Ezra 2:1). It may also be a way of extending the metaphor of plowing from the prior verse. To cut the cords might mean to sever the lines connecting the plow to the oxen. Either makes the same point: that the Lord upholds His vows (Genesis 12:1–3; 2 Samuel 7:16–17; Jeremiah 29:11–14).