Charles H. Spurgeon on Psalms 119:3

They also do no iniquity. Blessed indeed would those men be of whom this could be asserted without reserve and without explanation: we shall have reached the region of pure blessedness when we altogether cease from sin. Those who follow the word of God do no iniquity, the rule is perfect, and if it be constantly followed no fault will arise. Life, to the outward observer, at any rate, lies much in doing, and he who in his doings never swerves from equity, both towards God and man, has hit upon the way of perfection, and we may be sure that his heart is right. See how a whole heart leads to the avoidance of evil, for the Psalmist says, "That seek him with the whole heart. They also do no iniquity." We fear that no man can claim to be absolutely without sin, and yet we trust there are many who do not designedly, wilfully, knowingly, and continuously do anything that is wicked, ungodly, or unjust. Grace keeps the life righteous as to act even when the Christian has to bemoan the transgressions of the heart. Judged as men should be judged by their fellows, according to such just rules as men make for men, the true people of God do no iniquity: they are honest, upright, and chaste, and touching justice and morality they are blameless. Therefore are they happy.

They walk in his ways. They attend not only to the great main highway of the law, but to the smaller paths of the particular precepts. As they will perpetrate no sin of commission, so do they labour to be free from every sin of omission. It is not enough to them to be blameless, they wish also to be actively righteous. A hermit may escape into solitude that he may do no iniquity, but a saint lives in society that he may serve his God by walking in his ways. We must be positively as well as negatively right: we shall not long keep the second unless we attend to the first, for men will be walking one way or another, and if they do not follow the path of God's law they will soon do iniquity. The surest way to abstain from evil is to be fully occupied in doing good. This verse describes believers as they exist among us: although they have their faults and infirmities, yet they hate evil, and will not permit themselves to do it; they love the ways of truth, right and true godliness, and habitually they walk therein. They do not claim to be absolutely perfect except in their desires, and there they are pure indeed, for they pant to be kept from all sin, and to be led into all holiness.