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 henceforward 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 maketh all the stones of the altar as chalk stones - That is, Yahweh shall make the stones of the altars reared in honor of idols like chalk stones; or shall throw them down, and scatter them abroad 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 therein (see the note at Isaiah 17:8).