'Solid' in the Bible

I fed you milk, not solid food, for you were not yet ready. In fact, you are still not ready,

However, God's solid foundation remains standing, bearing this seal: "The Lord knows those who are his," and "Everyone who confesses the name of the Lord must turn away from evil."

For though you should in fact be teachers by this time, you need someone to teach you the beginning elements of God's utterances. You have gone back to needing milk, not solid food.

But solid food is for the mature, whose perceptions are trained by practice to discern both good and evil.