John Calvin Commentary Isaiah 26:3

"Thou wilt keep [him] in perfect peace, [whose] mind [is] stayed [on thee]; because he trusteth in thee." — Isaiah 26:3 (ASV)

The thought is fixed; you will keep peace, peace. As the Hebrew word יצר (Yĕtzĕr) signifies both “imagination” or “creature,” and “thought,” some render it, “By a settled foundation you will keep peace;” as if the Prophet meant, that when men, amidst the convulsions of the world, continue to rest firmly on God, they will always be safe.

Others render it, “For the fixed thought you will keep peace;” which amounts to nearly the same thing, that those who have fixed their minds on God alone will eventually be happy; for in no other way does God promise that he will be the guardian of his people unless they rely on his grace with settled thoughts, and without change or wavering.

Since, however, the sign of the dative case is not added, but the Prophet in a concise manner of expression says, “Fixed or steadfast thought,” let my readers judge if it is not more appropriate to view it as referring to God, so that the meaning is that the peace of the Church is founded on his eternal and unchangeable purpose; for, in order to prevent godly minds from continual wavering, it is of the highest importance to look to the heavenly decree.

It is undoubtedly true that we ought constantly to hope in God, so that we may perceive his continual faithfulness in defending us; and believers are always enjoined not to be driven about by any doubt, or uncertainty, or wavering, but firmly to rely on God alone. Yet the meaning which is more easily obtained from this passage, and comes more naturally from the words of the Prophet, is, that it is a fixed and unchangeable decree of God, that all who hope in him shall enjoy eternal peace; for if fixed thought means the certainty and steadfastness of the godly, it would be superfluous to assign the reason, which is —

Because he has trusted in you. In short, both modes of expression would have been harsh, that “continual peace is prepared for imagination,” or “for thought.” But it is perfectly appropriate to say that, when we trust in God, he never disappoints our hope, because he has determined to guard us forever. Hence it follows, that, since the safety of the Church does not depend on the state of the world, it is not moved or shaken by the various changes that happen daily; but that, having been founded on the purpose of God, it stands with steady and unshakable firmness, so that it can never fall.

There is also, I think, an implied contrast between God’s fixed thought and our wandering imaginations; for at almost every moment there springs up something new that drives our thoughts here and there, and there is no change, however slight, that does not produce some doubt. We ought therefore to hold this principle, that we do wrong if we judge God’s unshaken purpose by our fickle imaginations; as we will elsewhere see,

As far as the heavens are from the earth, so far are my thoughts from your thoughts, O house of Israel. (Isaiah 55:9)

We ought therefore above all to be certain, that our salvation is not liable to change; because the purpose of God is unchangeable.

You will keep peace, peace. What has now been stated explains the reason of the repetition of the word peace; for it denotes uninterrupted continuance forever. By the word peace I understand not only serenity of mind, but every kind of happiness; as if he had said, that the grace of God alone can enable us to live prosperously and happily.