A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 129:1The people of God, often delivered from enemies, are confident of His favor, by their overthrow in the future. (Psa 129:1-8)
may Israel now say--or, "oh! let Israel say" (Psa 124:1). Israel's youth was the sojourn in Egypt (Jer 2:2; Hos 2:15).
psa 129:2prevailed--literally, "been able," that is, to accomplish their purpose against me (Psa 13:4).
psa 129:3The ploughing is a figure of scourging, which most severe physical infliction aptly represents all kinds.
psa 129:4the cords--that is, which fasten the plough to the ox; and cutting denotes God's arresting the persecution;
psa 129:5The ill-rooted roof grass, which withers before it grows up and procures for those gathering it no harvest blessing (Rut 2:4), sets forth the utter uselessness and the rejection of the wicked.