Psalms 119:125

"I am Your servant. O grant me understanding, that I may know Your testimonies" [Psalm 119:125]. This petition must never be intermitted. For it suffices not to have received understanding, and to have learned the testimonies of God, unless it be evermore received, and evermore in a manner quaffed from the fountain of eternal light. For the testimonies of God are the better and the better known, the more understanding a man attains to.

The blessed David asks the Lord for that very understanding by which he can recognize God's commands, which he well knew were written in the book of the law, when he says "I am your servant: O give me understanding that I may learn your commandments." Certainly he was in possession of understanding, which had been granted to him by nature, and also had at his fingers' ends a knowledge of God's commands which were preserved in writing in the law. Still he prayed to the Lord that he might learn this more thoroughly because he knew that what came to him by nature would never be sufficient for him, unless his understanding was enlightened by the Lord by his daily illumination, to understand the law spiritually and to recognize his commands more clearly.

There has to be a distinction between the law and grace. The law knows how to command; grace, how to help. The law would not command if there were no free will, nor would grace help if the will were sufficient. We are commanded to have understanding when the Scripture says, "Do not become like the horse and the mule that have no understanding," yet we pray to have understanding when it says, "Give me understanding that I may learn your commandments." We are commanded to have wisdom when it says, "You fools, be wise at last," but we pray to have wisdom when it says, "If any of you want wisdom, let him ask of God who gives to all generously and without reproach." We are commanded to have continence when it says, "Be prepared for action," but we pray to have continence when it says, "As I knew that no one could be continent except God gave it, and this also was a point of wisdom to know whose gift it was, I went to the Lord and besought him." Finally, not to be too lengthy in listing all the rest, we are commanded not to do evil when it says, "Decline from evil," but we pray not to do evil when it says, "We pray the Lord that you do no evil." We are commanded to do good when it says, "Decline from evil and do good," but we pray to do good when it says, "We cease not to pray for you, asking," and among other things that he asks he mentions, "That you may walk worthy of God in all things pleasing, in every good work and good word." As then we acknowledge the part played by the will when these commands are given, so let him acknowledge the part played by grace when these petitions are offered.