John Gill

And I saw, when for all the causes, whereby backsliding Israel committed adultery,.... Not only Judah saw, but God, who sees all things, saw the idolatry of the ten tribes which apostatized from him, and all the springs, causes, reasons, and occasions of it, and its consequences; and also the treachery, hardness, and idolatry of Judah: I had put her away, and given her a bill of divorce; as men did, when they put away their wives, as they might lawfully do in case of adultery; and here being that which answered to it, spiritual adultery or idolatry, the Lord, who was married to this people, put them away from him, and caused them to be carried captive out of their own land into another, Kg2 17:6 which is meant by the bill of divorce; so the Targum, "I caused them to go into captivity, as those that give a bill of divorce (to their wives) and dismiss them:'' yet her treacherous sister Judah feared not; to commit idolatry and offend the Lord, nor stood in awe of his righteous judgments; had no reverence of God, nor fear of punishment; so hardened and daring was she: but went and played the harlot; committed idolatry, as the ten tribes did, taking no warning by what befell them.