Matthew Henry comments on Isaiah 26:3 —
1. This is here the matter of a promise (v. 3): Thou wilt keep him in peace, peace, in perfect peace, inward peace, outward peace, peace with God, peace of conscience, peace at all times, under all events; this peace shall he be put into, and kept in the possession of, whose mind is stayed upon God, because it trusts in him. It is the character of every good man that he trusts in God, puts himself under his guidance and government, and depends upon him that it shall be greatly to his advantage to do so. Those that trust in God must have their minds stayed upon him, must trust him at all times, under all events, must firmly and faithfully adhere to him, with an entire satisfaction in him; and such as do so God will keep in perpetual peace, and that peace shall keep them. When evil tidings are abroad those shall calmly expect the event, and not be disturbed by frightful apprehensions arising from them, whose hearts are fixed, trusting in the Lord, Ps. cxii. 7. 2. It is the matter of a precept (v. 4): “Let us make ourselves easy by trusting in the Lord for ever; since God has promised peace to those that stay themselves upon him, let us not lose the benefit of that promise, but repose an entire confidence in him. Trust in him for ever, at all times, when you have nothing else to trust to; trust in him for that peace, that portion, which will be for ever.” Whatever we trust to the world for, it will be but for a moment: all we expect from it is confined within the limits of time. But what we trust in God for will last as long as we shall last. For in the Lord Jehovah-Jah, Jehovah, in him who was, and is, and is to come, there is a rock of ages, a firm and lasting foundation for faith and hope to build upon; and the house built on that rock will stand in a storm. Those that trust in God shall not only find in him, but receive from him, everlasting strength, strength that will carry them to everlasting life, to that blessedness which is for ever; and therefore let them trust in him for ever, and never cast away nor change their confidence.