The prophet doth not dictate words, but sense to them, teaching them the matter of their prayer; first, by way of confession. Sin is called a transgression, because it is going aside from the way of God's precepts; it is called rebellion, because it is an act contrary to that allegiance and duty which we owe unto God, and the covenant we have made with him. By pardoning here is meant the discharge of the guilty persons from the temporal punishment due for sin (as it is often taken in Scripture); so it signifies, thou hast plagued us according to the just desert of our sins.
Related Commentaries of Lamentations 3:42
Lamentations 3:42
42 We have transgressed and have rebelled: thou hast not pardoned.