Charles H. Spurgeon on Psalms 50:15

Call upon me in the day of trouble, etc. The Lord hath promised his children supply of all good things, yet they must use the means of impetration; by prayer. He feed the young ravens when they call upon him. Ps 147:9. He feeds the young ravens, but first they call upon him. God withholds from them that ask not, lest he should give to them that desire not. (Augustine.) David was confident that by God's power he should spring over a wall; yet not without putting his own strength and agility to it. Those things we pray for, we must work for. (Augustine.) The carter in Isidore, when his cart was overthrown, would needs have his god Hercules come down from heaven, to help him up with it; but whilst he forbore to set his own shoulder to it, his cart lay still. Abraham was as rich as any of our aldermen, David as valiant as any of our gentlemen, Solomon as wise as any of our deepest naturians, Susanna as fair as any of our painted pieces. Yet none of them thought that their riches, valour, policy, beauty, or excellent parts could save them; but they stirred the sparks of grace, and bestirred themselves in pious work. And this is our means, if our meaning be to be saved. Thomas Adams.