Hebrews uses “milk” for basic teaching and “solid food” for mature understanding. It says solid food belongs to the mature, whose powers of discernment are trained by practice to distinguish good from evil (Hebrews 5:12–14). The contrast is about growth and discernment.
In Hebrews 5:11–12 the writer pauses his teaching because the audience is no longer able to take it in well. He says he has much more to explain, but it has become hard to communicate because they have grown unresponsive as listeners. This pause comes right as the writer is starting to develop a longer explanation about Jesus as high priest and his connection with Melchizedek (introduced immediately before in Hebrews 5:10 and resumed afterward in Hebrews 6:20). Instead of continuing, he addresses a problem in the audience’s capacity to learn.
Hebrews 5:11–12 is a deliberate pause in the author’s teaching. The writer says there is “much to say” about the current topic, but it is hard to communicate because the audience has “become dull of hearing” (a decline in listening/receptiveness). This is not framed as a lack of available truth, but a learning problem in the hearers.
A common mistake is to turn the wording into a slogan. The better reading keeps the phrase tied to the passage, the speaker, and the problem the book is addressing.
Start with Hebrews 5:12-14, then read the surrounding section so the answer stays connected to the passage's flow.
12For when by reason of the time you ought to be teachers, you again need to have someone teach you the rudiments of the first principles of the oracles of God. You have come to need milk, and not solid food.
13For everyone who lives on milk is not experienced in the word of righteousness, for he is a baby.
14But solid food is for full grown men, those who by reason of use have their senses exercised to discern good and evil.