Matthew Poole and continuators on Psalms 99:8

8 Thou answerdest them , O LORD our God: thou wast a God that forgavest them a, though thou tookest vengeance of their inventions .

The intercessours beforementioned. Either 1. Moses and Aaron, who did sin, and whose sins God did pardon, yet so as that he did punish them with exclusion from the land of Canaan; of which see Numb. 20. 12. Deut. 32. 50, 51. Or rather 2. the people for whom they prayed; which though not expressed may be easily understood from the following words and from the Histories to which these words relate. For this forgiving was evidently the effect of Gods answering the Prayers of the persons above mentioned. And therefore as their Prayers recorded in Scripture were not for the pardon of their own sins, but for the pardon of the peoples sins, so this forgiveness granted was for the sins of the people. And whereas the people are not here mentioned; it must be remembred that in Scripture the relative is frequently put without the antecedent, as it is Numb. 7. 89. and 114. 2. Prov. 14. 26.

This clause limits and explains the former. Thou didst forgive the sins of the people not absolutely and universally, for thou didst punish them severely, but so far as not to inflict that total and final destruction upon them which they deserved, and thou hadst threatned. See Exod. 32. 10, 14, 34.