For every one who uses milk, or, who partakes of milk, etc. He means those who from tenderness or weakness as yet refuse solid doctrine; for otherwise he who is grown up is not averse to milk. But he reproves here an infancy in understanding, such as constrains God even to prattle with us. He then says, that babes are not fit to receive the word of righteousness, understanding by righteousness the perfection of which he will presently speak. [1] For the Apostle does not here, as I think, refer to the question, how we are justified before God, but takes the word in a simpler sense, as denoting that completeness of knowledge which leads to perfection, which office Paul ascribes to the Gospel in his epistle to the Colossians, 1:28; as though he had said, that those who indulge themselves in their ignorance preclude themselves from a real knowledge of Christ, and that the doctrine of the Gospel is unfruitful in them, because they never reach the goal, nor come even near it.

Footnotes

1 - This is the view of Grotius and others, but some regard "the word of righteousness" as a paraphrasis for the Gospel; and Stuart renders it, "the word of salvation." Dr. Owen says that the Gospel is called "the word of righteousness," because it reveals the righteousness of God, Romans 1:17. It may also be so called, because it reveals and contains the truth, the full truth, partly revealed previously. The word "righteousness" has this meaning both in the Old and New Testaments. See Psalm 3:4; Isaiah 45:19, 23; and Matthew 21:23, 2-Corinthians 11:15. "The ministers of righteousness" in the last text are opposed to false ministers. -- Ed.

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 salvation by the Redeemer; see the notes on Romans 1:17.
For He is a babe - That is, in religious matters. He understands the great system only as a child may. It is common to speak of "babes in knowledge," as denoting a state of ignorance.

For every one that useth milk - It is very likely that the apostle, by using this term, refers to the doctrines of the law, which were only the rudiments of religion, and were intended to lead us to Christ, that we might be justified by faith.
The word of righteousness - Αογος δικαιοσυνης· The doctrine of justification. I believe this to be the apostle's meaning. He that uses milk - rests in the ceremonies and observances of the law, is unskilful in the doctrine of justification; for this requires faith in the sacrificial death of the promised Messiah.

For every one that useth milk [is] unskilful in the (l) word of righteousness: for he is a babe.
(l) In the word that teaches righteousness.

For everyone that useth milk,.... 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 discovering the agreement there is between the righteousness of Christ, and the justice of God; and of teaching men to live soberly, righteously, and godly: and such are unskilful in it, who either have no knowledge of the doctrine of justification; of the matter of it, Christ's righteousness; of the form of it, by imputation; and of the date of it, before faith: or have a very confused notion of it, joining their own works with Christ's righteousness, for justification, as many judaizing professors did; or who, if they have a notional knowledge of it, have no practical concern in it; do not believe with the heart unto righteousness; have not the experience, sweetness, and power of this doctrine upon them; and do not live lives agreeable to it:
for he is a babe. This word is used sometimes by way of commendation, and is expressive of some good characters of the saints; such as harmlessness and inoffensiveness, humility, and meekness, a desire after the sincere milk of the word, freedom from rancour and malice, hypocrisy and guile; but here it is used by way of reproach, and denotes levity and inconstancy, ignorance and non-proficiency, want of digestion of strong meat, and incapacity to take care of themselves, as standing in need of tutors and governors.

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" (Romans 1:17), and which is called "the ministration of righteousness" (2-Corinthians 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 Matthew 3:15).

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.