Vv. 33 and 34 are substantially identical in their prayer for enlightenment and their vow of obedience. Both are based on the conviction that outward revelation is incomplete without inward illumination. Both recognise the necessary priority of enlightened reason as condition of obedient action, and such action as the test and issue of enlightenment. Both vow that knowledge shall not remain barren. They differ in that the former verse pledges the psalmist to obedience unlimited in time and the latter to obedience without reservation. But even in uttering his vow the singer remembers his need of God's help to keep it, and turns it, in ver. 35, into petition, which he very significantly grounds on his heart's delight in the Law. Warm as that delight may be, circumstances and flesh will cool it, and it is ever a struggle to translate desires into deeds. Therefore we need the sweet constraint of our Divine Helper to make us walk in the right way. Again, in ver. 36 the preceding profession is caught up and modulated into petition. "Incline my heart" stands to "In it I delight," just as "Make me walk" does to "I will observe it." Our purest joys in God and in His Will depend on Him for their permanence and increase. Our hearts are apt to spill their affection on the earth, even while we would bear the cup filled to God. And one chief rival of "Thy testimonies" is worldly gain, from which there must be forcible detachment in order to, and as accompaniment of, attachment to God. All possessions which come between us and Him are "plunder," unjust gain.