In alluding to the elementary truths the writer employed an expression which could refer to the letters of the alphabet as they might be learned by a school child. “You seem to need your ABCs reviewed,” his rebuke suggested, but at the same time he had no intention of going over them (6:1). What he apparently had mainly in view was their wavering state of mind in regard to the error that sought to lure them away from the faith. If they were being urged, whether by sectarians or others, to abandon their Christian profession, then clearly this called into question the fundamental truths they should have been firm in. The result was, to all appearances, you need milk, not solid food! But what he would shortly offer them would be solid food indeed, by which he evidently hoped to pull them dramatically forward in their Christian experience.
Hodges, Z. C. (1985). Hebrews. In J. F. Walvoord & R. B. Zuck (Eds.), The Bible Knowledge Commentary: An Exposition of the Scriptures (Vol. 2, pp. 792–793). Wheaton, IL: Victor Books.