strive for masteries - “strive in the games” [Alford]; namely, the great national games of Greece.
yet is he not crowned, except - even though he gain the victory.
strive lawfully - observing all the conditions of both the contest (keeping within the bounds of the course and stript of his clothes) and the preparation for it, namely, as to self-denying diet, anointing, exercise, self-restraint, chastity, decorum, etc. (1Co 9:24-27).