Tempted, etc. This word is to be taken in a bad sense; it means to provoke in a proud and insulting manner, which we express in French by saying, defier comme en depitant For though God had often brought them help, yet they forgot all, and scornfully asked, where was his power. Proved, etc. This clause is to be thus explained, "When yet they had proved me and seen my works". For it enhanced the guilt of their impiety, that having been taught by so many evidences of divine power, they had made so bad a progress. For it was a marvelous supineness and stupidity to esteem God's power as nothing, which had been so fully proved. [1] Forty years. These are connected by David with what follows. But we know that the Apostles in quoting passages attend more to the general meaning than to the words. And no doubt God complained that the people had been vexatious to him for forty years, because so many benefits had availed nothing for the purpose of teaching them; for though God did good continually to them who were wholly unworthy, they yet never ceased to rise up against him. Hence arose his continual indignation, as though he had said "Not once or for a short time have they provoked me, but by their incessant wickedness for forty years." Generation means race, or men of one age.

Footnotes

1 - See [15]Appendix M.

Proved me - "As if they would have made an experiment how much it was possible for me to bear." - Doddridge. The meaning is: "they put my patience to a thorough trial."
And saw my works - That is, my miracles, or my interpositions in their behalf. They saw the wonders at the Red Sea, the descent on Mount Sinai, the supply of manna, etc., and yet while seeing those works they rebelled. Even while sinners look on the doings of God, and are surrounded by the proofs of his power and goodness, they rebel, and provoke him to anger. Men sin when God is filling their houses with plenty; when he opens his hand daily to supply their wants; when they behold the manifestations of his goodness on the sea and on the land; and even in the midst of all the blessings of redemption, they provoke him to wrath.
Forty years - The whole time during which they were passing from Egypt to the promised land. This may mean either that they saw his works forty years, or that they tempted him forty years. The sense is not materially affected whichever interpretation is preferred.

When your fathers tempted me - It would be better to translate οὑ where than when, as the Vulgate has done in its ubi; and this translation has been followed by Wiclif, Coverdale, Tindal, and our first translators in general. In my old MS. Bible the 7th, 8th, and 9th verses stand thus: -
Wherefore as the Holy Gost seith, to-day gif yhe han herde his voyce: nye yhe herden ghour hertis as in wrath-thinge, after the day of temptacioun in desert. Where ghoure fadris temptiden me: provyden and saiden my werkis. Wherefore fourtye yeere I was offendid or wrothe to this generatoun.
In behalf of this translation, Dr. Macknight very properly argues: "The word When implies that, at the time of the bitter provocation, the Israelites had seen God's works forty years; contrary to the history, which shows that the bitter provocation happened, in the beginning of the third year after the Exodus: whereas the translation where, as well as the matter of fact, represents God as saying, by David, that the Israelites tempted God in the wilderness during forty years, notwithstanding all that time they had seen God's miracles."

When your fathers tempted me,.... This the apostle cites and repeats, to expose the glorying of the Jews in their ancestors; to dissuade them from following their sinful practices; to deter them from the same by observing both their sin and punishment; and to heighten their regards to the voice and Gospel of Christ:
proved me; this is either an explication of the former phrase; or it may design the experience this people had of the power and goodness of God, notwithstanding their tempting and provoking the Lord by a distrust of them; which is an aggravation of their sin and ingratitude, and shows the forbearance of God, and that wicked men may partake of outward favours:
and saw my works forty years; that is, God's works of providence, in furnishing them with the necessaries of life, in guiding, protecting, and supporting them for the space of forty years, in the wilderness; and his miracles, and the punishment of their enemies; yet they saw and perceived not, but all this time sinned against the Lord, see Deuteronomy 29:2 the space of time, forty years, is in the psalm placed to the beginning of the next verse, and is joined with God's grief and indignation at the people, as it is also by the apostle, in Hebrews 3:17 but the people's sin, and God's grief at it, being of equal duration, it matters not to which it is placed, and therefore to both; perhaps, one reason of its being repeated, and so much notice taken of it is, because there was just this number of years from Christ's sufferings, to the destruction of Jerusalem; which the apostle might have in view.

When--rather, "Where," namely, in the wilderness.
your fathers--The authority of the ancients is not conclusive [BENGEL].
tempted me, proved me--The oldest manuscripts read, "tempted (Me) in the way of testing," that is, putting (Me) to the proof whether I was able and willing to relieve them, not believing that I am so.
saw my works forty years--They saw, without being led thereby to repentance, My works of power partly in affording miraculous help, partly in executing vengeance, forty years. The "forty years" joined in the Hebrew and Septuagint, and below, Hebrews 3:17, with "I was grieved," is here joined with "they saw." Both are true; for, during the same forty years that they were tempting God by unbelief, notwithstanding their seeing God's miraculous works, God was being grieved. The lesson intended to be hinted to the Hebrew Christians is, their "to-day" is to last only between the first preaching of the Gospel and Jerusalem's impending overthrow, namely, FORTY YEARS; exactly the number of years of Israel's sojourn in the wilderness, until the full measure of their guilt having been filled up all the rebels were overthrown.

Where your fathers - That hard - hearted and stiff - necked generation. So little cause had their descendants to glory in them. Tempted me - Whether I could and would help them. Proved me - Put my patience to the proof, even while they saw my glorious works both of judgment and mercy, and that for forty years.