Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
Deuteronomy Chapter 9
The lesson of this chapter is exactly that of Eph 2:8, "By grace are ye saved through faith; and that not of yourselves; it is the gift of God: not of works, lest any man should boast."
In referring to their various rebellions, Moses here, as elsewhere, has regard not so much for the order of time as to that of subject. (Compare Deu 1:9-15 note.) Such reasons as convenience and fitness to his argument sufficiently explain the variations observable when the statements of this chapter are minutely compared with those of Exo. 32-34. In these variations we have simply such treatment of facts as is usual and warrantable between parties personally acquainted with the matters.
So shalt thou drive them out, and destroy them quickly - This is not inconsistent with Deu 7:22, in which instant annihilation is not to be expected for the reasons assigned. Here Moses urges the people to trust in God's covenanted aid; since He would then make no delay in so destroying the nations attacked by them as to put them into enjoyment of the promises, and in doing so as fast as was for the well-being of Israel itself.
Also in Horeb - Rather, "even in Horeb." The time and circumstances made the apostasy at Horeb particularly inexcusable.
I fell down before the Lord, as at the first - Moses interceded for the people before he came down from the mountain the first time Exo 32:11-13. This intercession is only briefly alluded to in this verse. Afterward he spent another 40 days on the mountain in fasting and prayer to obtain a complete restitution of the covenant Exo 34:28. It is this second forty days, and the intercession of Moses made therein (compare Exo 34:9), that is more particularly brought forward here and in Deu 9:25-29.
Israel could not even boast that its heads and representatives continued, faithful. Aaron had been already designated for the high priestly functions; but he fell away with the rest of the people. It was due therefore solely to the grace of God and the intercession of Moses that Aaron himself and his promised priesthood with him were not cut off; just as at a later time, when Aaron had actually to die for a new sin Israel owed it still to the same causes that Eleazar was substituted and the High Priesthood perpetuated (compare Deu 10:6; Num 20:24-26).
See the marginal reference. Taberah was the name of a spot in or near the station of Kibroth-hattaavah, and accordingly is not named in the list of encampments given in Num 33:16. The separate mention of the two is, however, appropriate here, for each place and each name was a memorial of an act of rebellion. The instances in this and the next verse are not given in order of occurrence. The speaker for his own purposes advances from the slighter to the more heinous proofs of guilt.