bring . . . into subjection = reduce to slavery. Greek. doulagogeo. Only here. Compare App-190.
lest that by any means. Greek. mepos.
when, &c. = having preached. Greek. kerusso. App-121. There is an appropriateness in using here this verb, "to act as a herald". The herald summons the competitors.
be = become, or prove to be.
a castaway = disapproved, or rejected (for the prize). Greek. adokimos. See Rom_1:28.