Charles H. Spurgeon on Psalms 119:34

Give me understanding, and I shall keep thy law. This is the same prayer enlarged, or rather it is a supplement which intensifies it. He not only needs teaching, but the power to learn: he requires not only to understand, but to obtain an understanding. How low has sin brought us; for we even lack the faculty to understand spiritual things, and are quite unable to know them till we are endowed with spiritual discernment. Will God in very deed give us understanding? This is a miracle of grace. It will, however, never be wrought upon us till we know our need of it; and we shall not even discover that need till God gives us a measure of understanding to perceive it. We are in a state of complicated ruin, from which nothing but manifold grace can deliver us. Those who feel their folly are by the example of the Psalmist encouraged to pray for understanding: let each man by faith cry, "Give me understanding." Others have had it, why may it not come to me? It was a gift to them; will not the Lord also freely bestow it upon me?

We are not to seek this blessing that we may be famous for wisdom, but that we may be abundant in our love to the law of God. He who has understanding will learn, remember, treasure up, and obey the commandment of the Lord. The gospel gives us grace to keep the law; the free gift leads us to holy service; there is no way of reaching to holiness but by accepting the gift of God. If God gives, we keep; but we never keep the law in order to obtaining grace. The sure result of regeneration, or the bestowal of understanding, is a devout reverence for the law and a resolute keeping of it in the heart. The Spirit of God makes us to know the Lord and to understand somewhat of his love, wisdom, holiness, and majesty; and the result is that we honour the law and yield our hearts to the obedience of the faith.

Yea, I shall observe it with my whole heart. The understanding operates upon the affections; it convinces the heart of the beauty of the law, so that the soul loves it with all its powers; and then it reveals the majesty of the lawgiver, and the whole nature bows before his supreme will. An enlightened judgment heals the divisions of the heart, and bends the united affections to a strict and watchful observance of the one rule of life. He alone obeys God who can say, "My Lord, I would serve thee, and do it with all my heart"; and none can truly say this till they have received as a free grant the inward illumination of the Holy Ghost. To observe God's law with all our heart at all times is a great grace, and few there be that find it; yet it is to be had if we will consent to be taught of the Lord.

Observe the parallel of Psalms 119:2 and Psalms 119:10 where the whole heart is spoken of in reference to seeking, and in Psalms 119:58 in pleading for mercy; these are all second verses in their octonaries. The frequent repetition of the phrase shows the importance of undivided love: the heart is never whole or holy till it is whole or united. The heart is never one with God till it is one within itself.