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.