Hebrews 3:9

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 29:2-8 ) 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.