I will run the way of thy commandments. The meaning of the prophet is, that when God shall inspire him with love for his la he will be vigorous and ready, nay, even steady, so as not to faint in the middle of his course. His words contain an implied admission of the supineness inability of men to make any advancement in well-doing until God enlarge their hearts. No sooner does God expand their hearts, than they are fitted not only for walking, but also for running in the way of his commandments. He reminds us that the proper observance of the law consists not merely in external works, -- that it demands willing obedience, so that the heart must, to some extent, and in some way, enlarge itself. Not that it has the self-determining power of doing this, but when once its hardness and obstinacy are subdued, it moves freely without being any longer contracted by its own narrowness. Finally, this passage tells us, when God has once enlarged our hearts, there will be no lack of power, because, along with proper affection, he will furnish ability, so that our feet will be ready to run.

I will run the way of thy commandments - That is, I will not merely keep them - which might be expressed by "I will walk in them," but I will hasten to keep them; I will do it with alacrity, as when one runs to accomplish an object. I will devote to them all the energies of my life.
When thou shalt enlarge my heart - Or, more literally, "For thou wilt enlarge my heart;" expressing confidence that God would do this, so that he would be thus inclined and enabled to keep his commandments. it is an acknowledgment of dependence, and at the same time the expression of a confident belief that God would grant him the grace needful for him. The phrase "to enlarge the heart" means to make it free; to deliver it from all hindrances to what is right; to fill it with noble and holy purposes; to stimulate and animate it. The heart is contracted or made narrow by selfishness, pride, vanity, ambition, covetousness; it is made large by charity, love, hope, benevolence. Sin narrows the soul; religion enlarges it.

I will run - The particle כי elci, which we translate when, should be translated because: Because thou shalt enlarge, or dilate, my heart; make plain my path by cleansing me from my impurity, and taking the hinderances out of my way. I will then run without dread of stumbling, and every day make sensible progress.

I will run the way of thy commandments, when thou shalt (e) enlarge my heart.
(e) By this he shows that we can neither choose good, cleave to God's word, nor turn forward in his way, unless he make our hearts large to receive grace, and willing to obey.

I will run the way of thy commandments,.... Not only walk but run in it; which is expressive of great affection to the commands of God, of great readiness and cheerfulness, of great haste and swiftness in the way of them, and of great delight and pleasure therein;
when thou shall enlarge my heart; with the knowledge of God, his word, ways, worship, and ordinances; with his love more fully made known, and with an increase of love to him; with the fear of him, and a flow of spiritual joy and peace; and when delivered from straits and difficulties, from weights and pressures, and everything that may hinder walking or running; and being in circumstances which may lead and encourage to the one as to the other; see 1-Kings 4:29, Isaiah 60:5.

Run - I will obey thy precepts with all readiness, fervency, and diligence. Enlarge - When thou shalt replenish my heart with wisdom, and love to thee and thy law.