Hebrews 5:13

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 - 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.

5:13 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.