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.

I sware

Numbers 14:23,28-30 Surely they shall not see the land which I swore to their fathers, neither shall any of them that provoked me see it...

Deuteronomy 1:34,35 And the LORD heard the voice of your words, and was wroth, and swore, saying...

Hebrews 3:11,18 So I swore in my wrath, They shall not enter into my rest.)...

Hebrews 4:3,5 For we which have believed do enter into rest, as he said, As I have sworn in my wrath, if they shall enter into my rest...

that they should not enter. Heb. if they enter
my rest

Genesis 2:2,3 And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made...

Jeremiah 6:16 Thus said the LORD, Stand you in the ways, and see, and ask for the old paths, where is the good way, and walk therein...

Matthew 11:28,29 Come to me, all you that labor and are heavy laden, and I will give you rest...

Hosea 4:4-11 Yet let no man strive, nor reprove another: for your people are as they that strive with the priest...

Revelation 14:13 And I heard a voice from heaven saying to me, Write, Blessed are the dead which die in the Lord from now on: Yes, said the Spirit...

Covenanting a Duty.
The exercise of Covenanting with God is enjoined by Him as the Supreme Moral Governor of all. That his Covenant should be acceded to, by men in every age and condition, is ordained as a law, sanctioned by his high authority,--recorded in his law of perpetual moral obligation on men, as a statute decreed by him, and in virtue of his underived sovereignty, promulgated by his command. "He hath commanded his covenant for ever."[171] The exercise is inculcated according to the will of God, as King and …
John Cunningham—The Ordinance of Covenanting

Psalms
The piety of the Old Testament Church is reflected with more clearness and variety in the Psalter than in any other book of the Old Testament. It constitutes the response of the Church to the divine demands of prophecy, and, in a less degree, of law; or, rather, it expresses those emotions and aspirations of the universal heart which lie deeper than any formal demand. It is the speech of the soul face to face with God. Its words are as simple and unaffected as human words can be, for it is the genius …
John Edgar McFadyen—Introduction to the Old Testament