Jamieson, Fausset and Brown on Isaiah 55:7

7. unrighteous--Hebrew, "man of iniquity"; true of all men. The "wicked" sins more openly in "his way"; the "unrighteous" refers to the more subtle workings of sin in the "thoughts." All are guilty in the latter respect, thought many fancy themselves safe, because not openly "wicked in ways" (Psa 94:11). The parallelism is that of gradation. The progress of the penitent is to be from negative reformation, "forsaking his way," and a farther step, "his thoughts," to positive repentance, "returning to the Lord" (the only true repentance, Zec 12:10), and making God his God, along with the other children of God (the crowning point; appropriation of God to ourselves: "to our God"). "Return" implies that man originally walked with God, but has apostatized. Isaiah saith, "our God," the God of the believing Israelites; those themselves redeemed desire others to come to their God (Psa 34:8; Re 22:17).

abundantly pardon--Literally, "multiply to pardon," still more than "have mercy"; God's graciousness is felt more and more the longer one knows Him (Psa 130:7).