John Calvin Commentary Psalms 103:14

"For he knoweth our frame; He remembereth that we are dust." — Psalms 103:14 (ASV)

For he knoweth—David here annihilates all the worth that men would arrogate to themselves, and asserts that it is the consideration of our misery, and that alone, which moves God to exercise patience toward us. This, again, we should carefully note, not only for the purpose of subduing the pride of our flesh, but also so that a sense of our unworthiness may not prevent us from trusting in God. The more wretched and despicable our condition is, the more inclined God is to show mercy, for the remembrance that we are clay and dust is enough to incite him to do us good.

To the same purpose is the comparison immediately following (Psalms 103:15), that all the excellence of man withers away like a fading flower at the first blast of the wind. Man is indeed improperly said to flourish. But as it might be alleged that he is, nevertheless, distinguished by some endowment or other, David grants that he flourishes like the grass, instead of saying, as he might justly have done, that he is a vapor or shadow, or a thing of nothing.

Although, as long as we live in this world, we are adorned with natural gifts and, to say nothing of other things, live, and move, and have our being in God, (Acts 17:28); yet as we have nothing except what is dependent on the will of another, and which may be taken from us every hour, our life is only a show or phantom that passes away.

The subject treated here is properly the brevity of life, to which God has regard in pardoning us so mercifully, as it is said in another psalm: He remembered that they were but flesh, a wind that passeth away, and cometh not again, (Psalms 78:39).

If it is asked why David, making no mention of the soul (which is yet the principal part of man), declares us to be dust and clay, I answer that it is enough to induce God mercifully to sustain us when he sees that nothing surpasses our life in frailty.

And although the soul, after it has departed from the prison of the body, remains alive, yet its doing so does not arise from any inherent power of its own. Were God to withdraw his grace, the soul would be nothing more than a puff or blast, just as the body is dust; and thus there would doubtless be found in the whole man nothing but mere vanity.