From the additional notes to The Treasury of David, by Charles Spurgeon, in relation to Psalm 119.
Verse. 3. They do no iniquity. All such as are renewed by grace, and reconciled to God by Christ Jesus; to these God imputeth no sin to condemnation, and in his account they do no iniquity. Notable is that which is said of David, "He kept my commandments, and followed me with all his heart, and did that only which was right in mine eyes" (1 Kings 14:8). How can that be? We may trace David by his failings, they are upon record everywhere in the word; yet here a veil is drawn upon them; God laid them not to his charge. There is a double reason why their failings are not laid to their charge. Partly, because of their general state, they are in Christ, taken into favour through him, and "there is no condemnation to them that are in Christ" (Romans 8:1), therefore particular errors and escapes do not alter their condition; which is not to be understood as if a man should not be humbled, and ask God pardon for his infirmities; no, for then they prove iniquities and they will lie upon record against him. It was a gross fancy of the Valentinians, who held that they were not defiled with sin, whatsoever they committed; though base and obscene persons, yet still they were as gold in the dirt. No, no, we are to recover ourselves by repentance, to sue out the favour of God. When David humbled himself, and had repented, then saith Nathan, "The Lord hath put away thy sin" (2 Samuel 12:13). Partly, too, because their bent and habitual inclination is to do otherwise. They set themselves to comply with God's will, to seek and serve the Lord, though they are clogged with many infirmities. A wicked man sinneth with deliberation and delight, his bent is to do evil, he makes "provision for lusts" (Romans 13:14), and "serves" them by a voluntary subjection (Titus 3:3). But those that are renewed by grace are not "debtors" to the flesh, they have taken another debt and obligation, which is to serve the Lord (Romans 8:12).
Partly, too, because their general course and way is to do otherwise. Everything works according to its form; the constant actions of nature are according to the kind. So the new creature, his constant operations are according to grace. A man is known by his custom, and the course of his endeavours shows what is his business. If a man be constantly, easily, frequently carried away to sin, it discovers the habit of his soul, and the temper of his heart. Meadows may be overflowed, but marsh ground is drowned with every return of the tide. A child of God may be occasionally carried away, and act contrary to the inclination of the new nature; but when men are drowned and overcome by the return of every temptation, it argues a habit of sin.
And partly, because sin never carries sway completely, but it is opposed by dislikes and resistances of the new nature. The children of God make it their business to avoid all sin, by watching, praying, mortifying: "I said I will take heed to my ways, that I sin not with my tongue" (Psalms 39:1), and thus there is a resistance of the sin. God hath planted graces in their hearts, the fear of his Majesty, that works a resistance; and therefore there is not a full allowance of what they do. This resistance sometimes is more strong, then the temptation is overcome: "How can I do this wickedness, and sin against God?" (Genesis 39:9). Sometimes it is more weak, and then sin carries it, though against the will of the holy man: "The evil which I hate, that do I" (Romans 7:15; Romans 7:18). It is the evil which they hate; they protest against it; they are like men which are oppressed by the power of the enemy. And then there is a remorse after the sin: David's heart smote him. It grieves and shames them that they do evil. Tenderness goes with the new nature: Peter sinned foully, but he went out and wept bitterly. Thomas Manton.