Isaiah
Isaiah 40:29ESV·traditional attribution

He gives power to the faint, and to him who has no might he increases strength.

John Calvin Reformed @genevareformer

29. He giveth power to the faint. The Prophet now applies to the present subject the general statements which he made; for we have said that his intention was to give warmer encouragement to the people, and to lead them to cherish better hope.

Matthew Henry Presbyterian @wholebiblehenry

Here, I. The prophet reproves the people of God, who are now supposed to be captives in Babylon for their unbelief and distrust of God, and the dejections and despondencies of their spirit under their affliction (Isa 40:27): "Why sayest thou, O Jacob! to thyself and to those about thee, My way is hidden from the Lord?

Commenting on Isaiah 40:27-31

John Gill Reformed Baptist @doctorgill

Even the youths shall faint and be weary,.... Such as are in the prime of their strength, and glory in it, yet through the hand of God upon them, by one disease or another, their strength is weakened in the way; or they meet with that which they are not equal to, and sink under, and are discouraged, and obliged to desist.