Hebrews 5:13

“For everyone that useth milk, etc..] And sits down contented with the first principles of the Gospel, such as are easily taken in and digested; or makes use of the ceremonial law, as a schoolmaster to teach him the Gospel: is unskilful in the word of righteousness; the Gospel, which is a doctrine of righteousness; not of works of righteousness done by men, and of justification by them, or of a man's own righteousness; but of the pure, perfect, and everlasting righteousness of Christ: and it is called so, because it is the means of stripping a man of his own righteousness; and of revealing the righteousness of Christ unto him; and of working faith in him to lay hold upon it; and of…”

“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).”

“For every one that useth milk - Referring to the food of children. The apostle has in view here those Christians who resemble children in this respect, that they are not capable of receiving the stronger food adapted to those of mature age. Is unskilful - Inexperienced; who has not skill to perform anything. The word is properly applied to one who has not experience or skill, or who is ignorant. Here it does not mean that they were not true Christians - but that they had not the experience or skill requisite to enable them to understand the higher mysteries of the Christian religion. In the word of righteousness - The doctrine respecting the way in which men become righteous, or the way of…”

“Every one that useth milk - That neither desires, nor can digest, anything else: otherwise strong men use milk; but not milk chiefly, and much less that only. Is unexperienced in the word of righteousness - The sublimer truths of the gospel. Such are all who desire and can digest nothing but the doctrine of justification and imputed righteousness. Hebrews 5:14”

“is unskilful: Gr. hath no experience the word: Psa 119:123; Rom 1:17, Rom 1:18, Rom 10:5, Rom 10:6; Co2 3:9; Ti2 3:16 he: Isa 28:9; Mat 11:25; Mar 10:15; Rom 2:20; Co1 13:11, Co1 14:20; Eph 4:14; Pe1 2:2 Hebrews 5:14”