'Solid' in the Bible

For though by this time you ought to be teachers [because of the time you have had to learn these truths], you actually need someone to teach you again the elementary principles of God’s word [from the beginning], and you have come to be continually in need of milk, not solid food.

But solid food is for the [spiritually] mature, whose senses are trained by practice to distinguish between what is morally good and what is evil.