There is good evidence to support either Revised Standard Version‘s I am thankful (also New Jerusalem Bible, New International Version) or Good News Bible‘s “I thank God” (also New Revised Standard Version; similarly Revised English Bible). The UBS Greek text includes “God” (in square brackets), so Good News Bible follows it. The difference, though, is so slight that Good News Bible does not think it worth indicating in a footnote. Everywhere else Paul uses the full expression “I thank God.” So it would be natural for scribes to add “God” in this verse to make it agree with the other passages, and to fill out the meaning. The phrase “I thank” would be very clumsy in English by itself, and Paul certainly means something more specific than “I am thankful,” as Good News Bible makes clear.

Quoted with permission from Ellingworth, Paul and Hatton, Howard A. A Handbook on Paul’s First Letter to the Corinthians, 2nd edition. (UBS Handbook Series). New York: UBS, 1985/1994. For this and other handbooks for translators see here .