Jamieson, Fausset & Brown

useth--Greek, "partaketh," that is, taketh as his portion. Even strong men partake of milk, but do not make milk their chief, much less their sole, diet. the word of righteousness--the Gospel wherein "the righteousness of God is revealed from faith to faith" (Rom 1:17), and which is called "the ministration of righteousness" (Co2 3:9). This includes the doctrine of justification and sanctification: the first principles, as well as the perfection, of the doctrine of Christ: the nature of the offices and person of Christ as the true Melchisedec, that is, "King of righteousness" (compare Mat 3:15).