For every one that useth milk is unskilful in the word of righteousness: for he is a babe.
Useth, х metechoon (G3348)] - 'partaketh of.' 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 "is the righteousness of God revealed from faith to faith" (Romans 1:17); "the ministration of righteousness" (2 Corinthians 3:9). This includes 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 Melchisedek - i:e., "King of righteousness" (cf. Matthew 3:15).