Charles Ellicott Commentary Psalms 81:7

"Thou calledst in trouble, and I delivered thee; I answered thee in the secret place of thunder; I proved thee at the waters of Meribah. Selah" — Psalms 81:7 (ASV)

You called. —The recital of God’s past dealings with the people, usual at the Feast of the Tabernacles (Deuteronomy 31:10–13; Nehemiah 8:18), appears to follow here as if the feast were actually in progress and the crowd were listening to the psalmist.

I answered you in the secret place of thunder. —Mr. Burgess is undoubtedly right in taking the verb as from ânan, “to cover,” instead of ânah, “to answer.” I sheltered you in the thundercloud, with plain allusion to the “cloudy pillar.” The same verb is used in Psalms 105:39, He spread out the cloud for a covering.