Albert Barnes Commentary Psalms 119:3

"Yea, they do no unrighteousness; They walk in his ways." — Psalms 119:3 (ASV)

They also do no iniquity - See the notes at 1 John 3:9. The meaning is that they are righteous; their character is that they do what is right. It cannot mean that all persons who are religious are actually and absolutely perfect—for no one would hold this opinion; no one does hold it. It is general language such as is commonly used to describe an upright or righteous man. The declaration is true of all who are the friends of God—or, who are truly religious—in the following senses:

1. That they are habitually and characteristically righteous;
2. That they intend to do right—for a man who deliberately purposes to do wrong, to lead a life of sin and disobedience, cannot be a pious man.
3. That when they do err, it is not the result of intention or the design of their life, but because they are tempted, are overcome with passion, or are led by the power of their native corruption of heart to act contrary to their better judgment and their true character.

See Romans 7:14-17.

On the other hand, it is true that a man who is not characteristically righteous, who is not an upright man in his dealings, and who is not true, and honest, and temperate, and just, and benevolent, cannot be a child of God and heir of heaven.

No exactness of orthodoxy, no fervour of emotion, and no zeal in the cause of religion can constitute true piety without this.

They walk in his ways - Habitually, constantly, characteristically. They are not merely honest, upright, and just in their dealings with men, but they walk in the ways of God; they are religious.