Radak

Lead me, O Lord, in Thy righteousness: – This is my prayer unto Thee, that Thou shouldest lead me in Thy righteousness, meaning that Thou shouldest help me to go in the way of righteousness and justice, and lead me in it so that I may not stumble. Because of my watchful foes: – That they may not be able to rejoice over me through my stumbling, make straight Thy way before my face. And my watchful foes (שׁררי) – is the equivalent of “my enemies,” and is derived from (the verb) “I spy him (אשׁורנו), but not nigh” (Num. 24:17), because he is looking for evil, as (in the verse) “Saul eyed David” (1 Sam. 18:9). And this prayer is that He (God) should deliver him from faults and from deliberate sins, as he says (in the verses Ps. 19:13, 14): “Clear me from hidden (faults); moreover, from deliberate sins restrain Thy servant.” Make Thy way plain before my face: – הישׁר (“make plain”) has the yodh of the first radical pronounced, unlike verbs in which the first radical is quiescent; and a similar case to it is אתך היצא (“Bring forth with thee,” Gen. 8:17). And Kethib has waw on the analogy of verbs with the first radical quiescent; and so with the pathah of the second radical (הושר הישַׁר), as also (in the verse): “Cause Thy mighty ones to come down (המחת), O Lord” (Joel 4:11).