Albert Barnes Commentary 1 Thessalonians 3:9

"For what thanksgiving can we render again unto God for you, for all the joy wherewith we joy for your sakes before our God;" — 1 Thessalonians 3:9 (ASV)

For what thanks can we render to God again? That is, what expression of thanksgiving can we render to God that shall be an equivalent for the joy which your holy walk has furnished, or which shall suitably express our gratitude for it.