Psalms 119:34

Give me understanding, and I shall keep thy law,.... A spiritual understanding; an understanding of the law, the perfection, purity, holiness, and spirituality of it; an understanding of the Gospel, and of Christ and the things of Christ; from whom grace and strength are to be had for the due observance of the law, as in his hands; which understanding must be given, and is a gift of pure, free, rich grace, to such who have it; though they cannot keep the law perfectly, as no mere man can, yet will keep it spiritually, from a principle of love and gratitude, and with a view to the glory of God and Christ, 1 John 5:20;

yea, I shall observe it with [my] whole heart; not only externally, and to be seen of men, and get applause from them; but doing the will of God from the heart, and with a good will and heartily, as to the Lord, and not to men; with a sincere affection for him, and with a single eye to his glory, Ephesians 6:6.