Albert Barnes Commentary Hebrews 3:17

"And with whom was he displeased forty years? was it not with them that sinned, whose bodies fell in the wilderness?" — Hebrews 3:17 (ASV)

But with whom was he grieved forty years? With whom was he angry?

Was it not with them that had sinned? They had sinned in various ways — by rebellion, murmuring, and unbelief. As God was angry with them for their sins, we have the same reason to anticipate that he will be angry with us if we sin. We should, therefore, be on our guard against the unbelief that would lead us to depart from him (Hebrews 3:12).

Whose carcases fell (Numbers 14:29). That is, they all died and were left on the sands of the desert. The whole generation was strewn along 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 died in this way were excluded from heaven.

Moses and Aaron were among 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. However, at different times, they all seem to have shared in the prevalent feelings of discontent and were all involved in the sweeping condemnation that they should die in the wilderness.