Albert Barnes Commentary 2 John 1:11

"for he that giveth him greeting partaketh in his evil works." — 2 John 1:11 (ASV)

For he that biddeth him, God speed, is partaker of his evil deeds. This shows that he countenances and approves of the doctrine which is taught. Compare to 1 Timothy 5:22 (see Barnes' commentary on this passage).

The word "speed" (in "God speed") means "wishes him success." The word "partaker" is used in connection with 1 Timothy 5:22.