'Solid' in the Bible

For although, considering the long time you have been believers, you ought now to be teachers of others, you really need some one to teach you over again the very rudiments of the truths of God, and you have come to require milk instead of solid food.

Such persons are mere babes. But solid food is for adults--that is, for those who through constant practice have their spiritual faculties carefully trained to distinguish good from evil.