1 Corinthians 9:27

but I keep under my body Literally, I strike under the eye, I beat black and blue. So the ancient Latin version of Irenæus renders it Corpus meum lividum facio. The Vulgate, less forcibly, castigo. Tyndale, tame. The same word is used in St Luke 18:5 of the effect of the repeated complaints of the poor widow. Cf. Shakespeare, King John, Acts 11. sc. 1, "Bethumpedwith words."

and bring it into subjection Literally, lead it into slavery. The body was to be the absolute property of the spirit, to obey its directions implicitly, as a slave those of its master. Romans 6:19. By a series of violent blows on the face, as it were, it was to be taught to submit itself to the dictates of its superior.

lest … when I have preached to others, I myself should be a castaway Castaway, Gr. ἀδόκιμος, one regarded as unworthy. Except in Hebrews 6:8, this word is everywhere else translated reprobatein the New Testament, and so here in the Vulgate reprobus. Wiclif, repreuable. No strength of religious conviction, we are here warned, can supply the place of that continuous effort necessary to make our calling and election sure." Some have regarded the word -preached" here (literally, heralded) as having a reference to the herald who proclaimed die victor in the games. Dean Stanley reminds us that the victor sometimes announced his own success, and that Nero did so (cf. Suetonius, Nero, c. 24) a short time after this Epistle was written. But this somewhat misses the point of the Apostle's meaning, which, if it is to be regarded as keeping up the metaphor derived from the games, is, that after having, as herald, proclaimed the victory of others, he himself contends and is worsted.