John Trapp on Isaiah 27:9

Ver. 9. By this therefore ſhall the iniquity of Jacob be purged] Hac re, i. e. deportatione in Babyloniam, ſaith Piſcator: By this, that is, by their being carried captive into Babylon, as it was made a means to bring the Elect to repentance. As one poyſon is antidotary to another: ſo is Affliction to ſin. Croſſes are Leeches to ſuck out the noxious blood: Flails to threſh off our husks: Files to brighten out graces, &c. Sanctfied afflictions (ſaid Mr. Dod) are good promotions. Corrections of Inſtructions are the way of life, Prov. 16.23. For though not joyous but grievous at preſent, yet afterwards they yield the peaceable fruit of righteouſneſs unto them that are thereby exerciſed, Heb. 12.11. It fareth with Gods afflicted, as it did once with thoſe that had the ſwearing ſickneſs in this land; If they ſlept they died: To keep them waking therefore, they were ſmitten with Roſemary-branches: whereat though they cried out, you kill me, you kill me, yet it proved a happy means to keep them alive. It was good for David that he was afflicted, Pſal. 119.71. it rid him of thoſe two evil humours, High mindedneſs and Earthly-mindedneſs, Pſal. 131.1.

And this is all the fruit] Gods rod, like Aarons, bloſſometh: and like that of Jonathan, it hath honey at the end of it. A good uſe and a good iſſue of afflictions is ever to be prayd for. I read of a gracious man, who lying under great torments of the Stone, would often cry out, The uſe, Lord, the uſe! And Mr. Perkins in like caſe deſired his friends to pray to God not ſo much for eaſe of his pain, as for increaſe of his faith and patience. Perdidiſti fructum afflictionum, ſaid Auſtin to ſome in his time, and it was a great loſs doubtleſs.

To take away his ſin] The ſin, not the man: D. Goodw. See Pſal. 99.8. A leprous or ulcerous member, a man loves as it is his own fleſh, Epheſ. 5.29. though he loatheth the corruption and putrefaction that is in it; therefore he cuts it not off, but plaiſtereth it: whereas a Wart or Wen he cutteth off, as not his fleſh: ſo here.

When he maketh all the ſtones of the Altar as Chalk-ſtones] When he, that is Jacob, in token of his true repentance, abandoneth all his mawmets and monuments of idolatry, and them aboliſheth and demoliſheth, ſo as never to be re-edified. The Jews after the captivity were ſo far from idolatry, that, they would not admit a Painter or Carver into their City. And how zealous they were to keep their Temple from ſuch defilement both in the time of Antiochus Epiphanes, and of the Romans, Hiſtories ſhew us.