But with whom was he grieved, or angry, etc. He means that God had never been angry with his people except for just causes, as Paul also reminds us in 1-Corinthians 10:5, 6. Therefore as many chastisements of God as we read were inflicted on the ancient people, so many grievous sins shall we find which provoked God's vengeance. At the same time we must come to this conclusion, that unbelief was the chief of all their evils; for though he mentions this the last, he yet means that it was the primary cause of their curse; and no doubt from the time they once became unbelievers, they never ceased to add one sin to another, and thus they brought on themselves new scourges continually. Hence those very persons who through unbelief rejected the possession of the land offered to them, pursued their own obstinacy, now lusting, then murmuring, now committing adultery, then polluting themselves with heathen superstitions, so that their depravity became more fully manifested. The unbelief, then, which they showed from the beginning, prevented them from enjoying the kindness of God; for the contempt of his word ever led them to sin. And as at first they deserved through their unbelief that God should deprive them of the promised rest, so whatever sin they committed afterwards flowed from the same fountain. It may be further asked, whether Moses, and Aaron, and those like them, were included in this number? To this I answer, that the Apostle speaks of the whole community rather than of individuals. It is certain that there were many godly men who were either not entangled in the general impiety or soon repented. Moses' faith was once shaken and only once, and that for a moment. The Apostle's words, therefore, contain a statement of the whole instead of a part, a mode of speaking frequently employed when a multitude or body of people are spoken of.

But with whom was he grieved forty years? - With whom was he angry; see the notes at Hebrews 3:10.
Was it not with them that had sinned - That had sinned in various ways - by rebellion, murmuring, unbelief. As God was angry with them for their sins, we have the same reason to apprehend that he will be angry with us if we sin; and we should, therefore, be on our guard against that unbelief which would lead us to depart from him; Hebrews 3:12.
Whose carcasses fell - Numbers 14:29. That is, they all died, and were left on the sands of the desert. The whole generation was strewed along in the way to Canaan. All of those who had seen the wonders that God had done "in the land of Ham;" who had been rescued in so remarkable a manner from oppression, were thus cut down, and died in the deserts through which they were passing; Numbers 26:64-65. Such an example of the effects of revolt against God, and of unbelief, was well suited to admonish Christians in the time of the apostle, and is suited to admonish us now, of the danger of the sin of unbelief. We are not to suppose that all of those who thus died were excluded from heaven. Moses and Aaron were among the number of those who were not permitted to enter the promised land, but of their piety there can be no doubt; Beyond all question, also, there were many others of that generation who were truly pious. But at different times they seem all to have partaken of the prevalent feelings of discontent, and were all involved in the sweeping condemnation that they should die in the wilderness.

But with whom was he grieved forty years? - I believe it was Surenhusius who first observed that "the apostle, in using the term forty years, elegantly alludes to the space of time which had elapsed since the ascension of our Lord till the time in which this epistle was written, which was about forty years." But this does not exactly agree with what appears to be the exact date of this epistle. However, God had now been a long time provoked by that race rejecting the manifested Messiah, as he was by the conduct of their forefathers in the wilderness; and as that provocation was punished by a very signal judgment, so they might expect this to be punished also. The analogy was perfect in the crimes, and it might reasonably be expected to be so in the punishment. And was not the destruction of Jerusalem a proof of the heinous nature of their crimes, and of the justice of God's outpoured wrath?
Whose carcasses fell - Ὡν τα κωλα επεσεν· Whose members fell; for τα κωλα properly signifies the members of the body, and here may be an allusion to the scattered, bleached bones of this people, that were a long time apparent in the wilderness, continuing there as a proof of their crimes, and of the judgments of God.

But with whom was he grieved forty years?.... As is said in Psalm 95:10; see Gill on Hebrews 3:10,
was it not with them that had sinned; not merely by committing personal iniquities, and particular provocations, which all men are guilty of, but by committing public sins; they sinned as a body of men; they joined together in the commission of sin; every sin is grieving to God, because it is contrary to his nature, is an act of enmity to him, is a transgression of his righteous law, and a contempt of his authority; but especially public sins, or the sins of a multitude, and when they are persisted in, which was the case of the Israelites; they sinned against him during the forty years they were in the wilderness; and so long was he grieved with them: the Alexandrian copy reads, "with them that believed not"; which points out the particular sin these men were guilty of, and which was so grieving to God, and suits well with the apostle's design:
whose carcasses fell in the wilderness? and so never entered into the land of Canaan. They died in the wilderness; and they did not die common and natural deaths, at least not all of them; their deaths were by way of punishment; in a way of wrath; in a judicial way: the Syriac version renders it, "their bones fell in the wilderness"; they lay scattered and unburied, and exposed to view, as an example of divine vengeance, see Numbers 14:29.

But--Translate, "Moreover," as it is not in contrast to Hebrews 3:16, but carrying out the same thought.
corpses--literally, "limbs," implying that their bodies fell limb from limb.