The youths are wearied and faint. By this comparison the Prophet illustrates more powerfully what he had formerly said, that the strength which God imparts to his elect is invincible and unwearied; for men's strength easily fails, but God's strength never fails. It is indeed certain that all the vigor which naturally dwells in us proceeds from God; but since men claim as their own what God has bestowed generally on all, the Prophet thus distinguishes between the strength of men which appears to be born with them, and that strength by which God peculiarly supports his elect; for God's kindness, which is diffused throughout all nature, is not sufficiently perceived. And thus by "men's strength" he means that which is generally possessed by mankind, and by "God's assistance," he means that by which he peculiarly assists us after our strength has failed; for the Prophet speaks of the grace of God which is cormmonly called supernatural, and says that it is perpetual, while men can have nothing in themselves but what is fading and transitory; that by this mark he may distinguish between the Church of God and the rest of the world, and between spiritual grace and earthly prosperity. And the young men by falling fall. In the former clause he made use of the word nrym, (negnarim,) youths, but now he adds vchrym, (bachurim,) which means not only that they were "young men," but also that they had been selected. [1] The repetition of the same statement may be supposed to refer particularly to age, though he means that they were persons of the choicest vigor and in the prime of life. With this design he recommends that excellent privilege which God bestows on his children in preference to other men; that they may be satisfied with their lot, and may bear no envy to earthly men, [2] for that strength of which they boast. In a word, he shews that men are greatly deceived if they are puffed up by confidence in their own strength, for they immediately sink and faint. He appears to allude to what happens every day, that the stronger any person is, the more boldly does he attempt what is exceedingly difficult, and the consequence is, that they who are naturally more robust seldom live to be old men. They think nothing too hard or difficult, they attempt everything, and rashly encounter all dangers; but they give way in the middle of their course, and suffer the punishment of their rashness. The same thing befalls those who are proud of any gift which God has bestowed on them, and are full of confidence in themselves; for all that they have received from God is reduced to nothing, or rather turns to their ruin and destruction; and thus they are justly punished for their insolence.

Footnotes

1 - "Men in full vigor, picked men, in military language." -- Stock.

2 - "Aux enfans de ce monde." "To the children of this world."

Even the youths shall faint - The most vigorous young men, those in whom we expect manly strength, and who are best suited to endure hardy toil. They become weary by labor. Their powers are soon exhausted. The design here is, to contrast the most vigorous of the human race with God, and to show that while all their powers fail, the power of God is unexhausted and inexhaustible.
And the young men - The word used here denotes properly "those who are chosen or selected" (בחוּרים bachûriym, Greek ἐκλεκτοὶ eklektoi), and may be applied to those who were selected or chosen for any hazardous enterprise, or dangerous achievement in war; those who would be selected for vigor or activity. The meaning is, that the most chosen or select of the human family - the most vigorous and manly, must be worn down by fatigue, or paralyzed by sickness or death; but that the powers of God never grow weary, and that those who trust in him should never become faint.

(f) Even the youths shall faint and be weary, and the young men shall utterly fall:
(f) They who trust in their own virtue, and do not acknowledge that all comes from God.

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. Some think the Babylonians and Chaldeans are here meant, the enemies of Israel, and by whom they were carried captive. The Targum interprets this clause, as well as the following, of wicked and ungodly men; and so do Jarchi and Kimchi: it may be applied to the Heathen emperors, who persecuted the church of God, and were smitten by him, and found it too hard a work to extirpate Christianity out of the world, which they thought to have done; and also to all the antichristian states, who have given their power and strength to the beast:
and the young men shall utterly fail; or, "falling shall fall" (f); stumble and fall, die and perish; or, however, not be able to perform their enterprise.
(f) "corruendo corruent", Montanus; "labefacti cadent", Castalio.

young men--literally, "those selected"; men picked out on account of their youthful vigor for an enterprise.

Faith is all that is needed to ensure a participation in the strength (עצמה after the form חכמה), which He so richly bestows and so powerfully enhances. "And youths grow faint and weary, and young men suffer a fall. But they who wait for Jehovah gain fresh strength; lift up their wings like eagles; run, and are not weary; go forward, and do not faint." Even youths, even young men in the early bloom of their morning of life (bachūrı̄m, youths, from בּחר, related to בּכר, בּגר), succumb to the effects of the loss of sustenance or over-exertion (both futures are defective, the first letter being dropped), and any outward obstacle is sufficient to cause them to fall (נכשׁל with inf. abs. kal, which retains what has been stated for contemplation, according to Ges. 131, 3, Anm. 2). In Isaiah 40:30 the verb stands first, Isaiah 40:30 being like a concessive clause in relation to Isaiah 40:31. "Even though this may happen, it is different with those who wait for Jehovah," i.e., those who believe in Him; for the Old Testament applies to faith a number of synonyms denoting trust, hope, and longing, and thus describes it according to its inmost nature, as fiducia and as hope, directed to the manifestation and completion of that which is hoped for. The Vav cop. introduces the antithesis, as in Isaiah 40:8. החליף, to cause one to pursue, or new to take the place of the old (Lat. recentare). The expression וגו יעלוּ is supposed by early translators, after the Sept., Targ. Jeremiah., and Saad., to refer to the moulting of the eagle and the growth of the new feathers, which we meet with in Psalm 103:5 (cf., Micah 1:16) as a figurative representation of the renewal of youth through grace. But Hitzig correctly observes that העלה is never met with as the causative of the kal used in Isaiah 5:6, and moreover that it would require נוצה instead of אבר. The proper rendering therefore is, "they cause their wings to rise, or lift their wings high, like the eagles" ('ēbher as in Psalm 55:7). Their course of life, which has Jehovah for its object, is as it were possessed of wings. They draw from Him strength upon strength (see Psalm 84:8); running does not tire them, nor do they become faint from going ever further and further.
The first address, consisting of three parts (Isaiah 40:1-11, Isaiah 40:12-26, Isaiah 40:27-31), is here brought to a close.

The youths - The youngest and strongest men, left to themselves.