Forty years long was I grieved with this generation, and said, It is a people that do err in their heart, and they have not known my ways: Forty years long - They did nothing but murmur, disbelieve, and rebel, from the time they began their journey at the Red Sea till they passed over Jordan, a period of forty years. During all this time God was grieved by that generation; yet he seldom showed forth that judgment which they most righteously had deserved.
It is a people that do err in their heart - Or, according to the Chaldee, These are a people whose idols are in their hearts. At any rate they had not God there.
They have not known my ways - The verb ידע yada, to know, is used here, as in many other parts of Scripture, to express approbation. They knew God's ways well enough; but they did not like them; and would not walk in them. "These wretched men," says the old Psalter, "were gifnen to the lufe of this lyfe: knewe noght my ways of mekenes, and charlte: for thi in my wreth I sware to thaim; that es, I sett stabely that if that sall entre in till my rest;" that is, they shall not enter into my rest.
This ungrateful people did not approve of God's ways - they did not enter into his designs - they did not conform to his commands - they paid no attention to his miracles - and did not acknowledge the benefits which they received from his hands; therefore God determined that they should not enter into the rest which he had promised to them on condition that, if they were obedient, they should inherit the promised land. So none of those who came out of Egypt, except Joshua and Caleb, entered into Canaan; all the rest died in the wilderness, wherein, because of their disobedience, God caused them to wander forty years.
It is well known that the land of Canaan was a type of heaven, where, after all his toils, the good and faithful servant is to enter into the joy of his Lord. And as those Israelites in the wilderness were not permitted to enter into the land of Canaan because of their unbelief, their distrust of God's providence, and consequent disobedience, St. Paul hence takes occasion to exhort the Jews, Hebrews 4:2-11, to accept readily the terms offered to them by the Gospel. He shows that the words of the present Psalm are applicable to the state of Christianity; and intimates to them that, if they persisted in obstinate refusal of those gracious offers, they likewise would fall according to the same example of unbelief - Dodd.