Give Thanks For God's Work In People's Lives
Whenever Paul uses 'ought' (Gk. opheilo), he is talking about a divinely inspired duty. He owed God a debt of gratitude for bringing the Thessalonians to faith in Jesus. Out of all the people in Thessalonica who heard the gospel, God chose some to be in the first 'harvest' in that city. They were the 'first-fruits' of the gospel. Exodus 23:16 says that the firstfruits should be brought to the Lord to thank Him for what He had done.