Thanks be unto God for his unspeakable gift.
His unspeakable gift - the gift of His own Son, which includes all other gifts (2 Corinthians 8:9; Romans 8:32). If we have received "His unspeakable gift," what great thing is it, if we give a few perishing gifts for His sake? It is this Gift which (the apostle already sees) ensures the completion of the Corinthians' gifts.