John Gill Commentary Psalms 106:6

"We have sinned with our fathers, We have committed iniquity, we have done wickedly." — Psalms 106:6 (ASV)

We have sinned with our fathers
Sinned in their first father Adam; derived a corrupt nature from their immediate ancestors; sinned after the similitude of their transgressions; sinned after their example, in like manner as they did; guilty of the same gross enormities as they were:

though sufficiently warned by the words of the prophets, and by punishments inflicted, they continued their sins, a constant series and course of them, and filled up the measure of their iniquities; they rose up in their stead an increase of sinful men, to augment the fierce anger of God, (Numbers 32:14) . And this the psalmist, in the name of the people of Israel, confesses, as it was his and their duty and interest so to do, (Leviticus 26:40) , and as we find it was usual with Old Testament saints, (Jeremiah 3:25) (14:20) (Daniel 9:8) .

We have committed iniquity, we have done wickedly ;
this heap of words is used to denote not only the multitude of their sins, but the aggravated circumstances of them; that they had committed all manner of sins, not sins of ignorance, frailty, and infirmity only; but presumptuous sins, sins against light and knowledge, grace and mercy; sins against both tables of the law, against God and their neighbour; and these attended with many aggravations: all which a sensible sinner is ready to make a frank and ingenuous confession of, and forsake; and such an one finds mercy with a God pardoning iniquity, transgression, and sin: this form of confession is followed by Solomon and Daniel, (1 Kings 8:47) (Daniel 9:5) .