As newborn babes. — The word “newborn” is, of course, newly, lately born, not born anew, although the birth meant is the new birth of 1 Peter 1:23. They are said to be still but newborn because they are still so far from maturity in Christ, as these sins testified. The metaphor is said to be not uncommon in Rabbinical writers to denote proselytes. St. Peter would, therefore, be describing Jews who had newly received the word of God, as proselytes of the new Israel. “As” means “in keeping with your character of.” (Comp. 1 Peter 1:14.)
Desire the sincere milk. — The word for “desire” here is a strong word — get an appetite for it. Bengel is perhaps right when he says on “newborn babes,” “It is their only occupation, so strong is their desire for it.” St. Peter here again seems to lend a thought to the writer to the Hebrews (Hebrews 5:12-14). In both places Jewish Christians are beginning to rebel against the Gospel instructions, and in both places they are warned that they have not yet outgrown the need of the very simplest elements of the Gospel. The epithet “sincere” should have been rendered guileless, as it contains a contrast with “guile” in the verse before; perhaps the intention of the epithet may be to rebuke the attempt to deal deceitfully with the Old Testament Scriptures after the example of the Septuagint passage quoted above.
Of the word. — This translation of the original adjective cannot possibly be right. The only other place in the New Testament where it is used, Romans 12:1, will show clearly enough its meaning here. There it is rendered “your reasonable service” — i.e., not “the service which may be reasonably expected of you,” but “the ritual worship which is performed by the reason, not by the body.” So here, “the reasonable guileless milk” will mean “the guileless milk which is sucked in, not by the lips, but by the reason.” The metaphor of milk (though used by St. Paul, 1 Corinthians 3:2) was not so hackneyed as now; and the Apostle wished to soften it a little, and explain it by calling it mental milk,” just as (so Huther points out) he explained the metaphor in 1 Peter 1:13, by adding “of your mind.” It is needless to add that the “mental milk” would, as a matter of fact, be “the milk of the word,” and that the Apostle is pressing his readers to cling with ardent attachment to the evangelical religion taught them by the Pauline party.
That ye may grow thereby. — All the best manuscripts and versions add “unto salvation,” which may confidently be adopted into the text. “Grow” is, of course, said in reference to the infant state of the converts as yet, and the maturity set before them (children long to be grown up) is spoken of as “salvation.” When we compare this with 1 Peter 1:18, we see that the perfect emancipation from Jewish superstitions is a main part of the “salvation” to which they are to grow up.