John Calvin Commentary Isaiah 1:27

"Zion shall be redeemed with justice, and her converts with righteousness." — Isaiah 1:27 (ASV)

Zion shall be redeemed with judgment. He confirms the same doctrine; and because the restoration of the Church was difficult to believe, he shows that it does not depend on human will, but is founded on the justice and judgment of God; as if he were saying that God will by no means permit his Church to be completely destroyed, because he is righteous.

The Prophet's purpose, therefore, is to withdraw the minds of the godly from earthly thoughts, so that in seeking the safety of the Church, they may depend entirely on God and not cease to maintain good hopes, even if, instead of help, they see nothing but obstacles. It is a great mistake to consider justice and judgment as referring to the Church, as if Isaiah were speaking about the well-ordered condition of a city; for, as I have stated, the plain meaning is that though people offer no assistance, the justice of God is fully sufficient to redeem his Church.

And indeed, as long as we look at ourselves, what hope are we entitled to cherish? On the contrary, how many things immediately present themselves that are suited to weaken our faith! It is only in the justice of God that we will find solid and lasting ground of confidence.

And they that return to her: this second clause points out the way of their deliverance; namely, that the exiles, who had been widely dispersed, will be gathered together again.