Albert Barnes Commentary Psalms 78:39

"And he remembered that they were but flesh, A wind that passeth away, and cometh not again." — Psalms 78:39 (ASV)

For he remembered that they were merely flesh—that they were human, that they were weak, that they were prone to err, that they were liable to fall into temptation. In his dealings with them, he took into view their fallen nature, their training, their temptations, their trials, their weaknesses, and he judged them accordingly. .

So it was with the Savior in his treatment of his disciples: The spirit indeed is willing, but the flesh is weak (Matthew 26:41). God will judge people as they are; he will not in his judgments forget that they are human, and that they are weak and feeble.

People often judge their fellow human beings with much more harshness, with much less allowance for their infirmities and weaknesses, than God shows in his dealings with humankind.

And yet such are the very people who are most ready to blame God for his judgments. If God acted on the principle and in the manner according to which they act, they could hope for no mercy from him. It is well for them that there is not one like themselves on the throne of the universe.

A wind that passes away and does not come again—which blows by us and is gone forever. What a striking description this is of a human being! How true of an individual! How true of a generation! How true of the race at large!

God remembers this when he thinks of people, and he deals with them accordingly. He is not harsh and severe, but kind and compassionate.

To a human being, so feeble—to the human race, so frail—to the generations of that race, so transitory, so soon passing off the stage of life—he is ever willing to show compassion. He does not make use of his great power to crush them; he prefers to manifest his mercy in saving them.