John Calvin Commentary Isaiah 10:20

"And it shall come to pass in that day, that the remnant of Israel, and they that are escaped of the house of Jacob, shall no more again lean upon him that smote them, but shall lean upon Jehovah, the Holy One of Israel, in truth." — Isaiah 10:20 (ASV)

It shall be in that day. Returning now to the elect people, he describes the result of the chastisement which was near.

Since it is painful and disagreeable for us to endure calamities and afflictions, and since we refuse them as much as is in our power, the Lord points out their result to us, so that we may be taught to consider their design and thus bear them more patiently. It is as if he had said, “You would wish that the Assyrians were driven to a great distance from you, and that you could live in comfort and safety. But consider that this chastisement is as necessary as medicine would be for curing your diseases, because you do not acknowledge the power of God, and you withdraw your confidence from him to give it to wicked men. It is truly wretched to place the hope of salvation in enemies and to rely on those who aim at nothing but your destruction.”

In the same way, Israel relied sometimes on the Assyrians and sometimes on the Egyptians.

But shall stay upon the Lord. We should not despise this compensation for the diminished numbers of the people: that the small portion which survived the calamity learned to place their hope in God. From this we see more clearly how necessary it was that God should chastise Israel. The mitigation he offers—that a remnant is still left, among whom the true worship of God is maintained—is suited to provide very great consolation.

In truth. This phrase is not unnecessary. Until the Lord had afflicted them, all wished to be considered the children of Abraham; all professed the faith and worshipped God without distinction. But it was mere pretense.

Isaiah therefore rebukes this hypocrisy and says that their hope will later be true and sincere, once they have been cleansed from deceptions. For although they very haughtily boasted of their confidence in God, they still continued to place their confidence in the assistance of the Assyrians.

Consequently, when they are chastised by their hand, they will learn to trust in God alone and will withdraw their heart from the assistance of men.

Therefore, understand that we cannot place our confidence in God unless we completely withhold our heart from created things. We should rely on God alone in such a way that we do not consider it a hardship to renounce all other grounds of confidence. When this perfect confidence does not exist, there is no room for truth; for the heart is divided and double (Psalms 12:2).