Thomas Aquinas, on Ps 33:20

“Many are the afflictions of the just; but out of them all will the Lord deliver them.”

“Then when he says, "The Lord guards," he shows how he delivers them so that they do not succumb. He says therefore, "The Lord guards all their bones." Just as sight resides in the eye, so in the bones and sinews resides strength; and therefore, just as sight is signified by the eye, so strength and power are signified by the bones: because just as the body is sustained by bones, so human life is sustained by virtues. In the future, therefore, he will deliver completely, but in the meantime he guards the bones, that is, the virtues, which profit more in weakness. Or, by "bones" are understood the perfect men, whom the Lord will guard: Ezek. 37: "Thus says the Lord God to these bones: Behold, I will send the spirit into you, and you shall live, and I will lay flesh upon you." "Not one of them shall be broken," because in tribulations no virtue of a person fails whom God guards. For charity did not fail in the saints through hatred, because they prayed for their persecutors; not meekness through anger, because no murmur resounded; not patience through injustice, indeed in their patience they possessed their souls. And therefore it is said of the paschal lamb, "You shall not break a bone of it," Ex. 12. Ps. 36: "When he falls, he shall not be dashed." Or, "Not one of these," namely of the predestined. Jn. 17: "None of them has perished except the son of perdition."”

Imported from an open dataset — not yet checked against the printed edition.