Albert Barnes Commentary Isaiah 27:9

"Therefore by this shall the iniquity of Jacob be forgiven, and this is all the fruit of taking away his sin: that he maketh all the stones of the altar as chalkstones that are beaten in sunder, [so that] the Asherim and the sun-images shall rise no more." — Isaiah 27:9 (ASV)

By this - This verse states the whole design of the punishment of the Jews. They were taken away from their temple, their city, and their land; they were removed from the groves and altars of idolatry by which they had been so often led into sin; and the design was to preserve them henceforth from relapsing into their accustomed idolatry.

The iniquity of Jacob - The sin of the Jewish people, and particularly their tendency to idolatry, which was their easily besetting sin.

Be purged - (see the note at Isaiah 1:25).

And this is all the fruit - And this is all the “object” or “design” of their captivity and removal to Babylon.

When he makes all the stones of the altar as chalk stones - That is, Yahweh will make the stones of the altars built in honor of idols like chalk stones, or will throw them down and scatter them like stones that are easily beaten to pieces.

The sense is that Yahweh, during their captivity in Babylon, would overthrow the places where they had worshipped idols.

The groves and images shall not stand up - The groves consecrated to idols, and the images erected in them (see the note at Isaiah 17:8).