Hebrews 5:12-14

Milk, then, is equivalent to the simpler, foundational material of God's word. Meat—those things that are more profound, mature and refined. A person who is only on milk, Paul says, is unskilled. Perhaps a more accurate translation would be "inexperienced" or "untried."

Consider this with a human child. Their diets are mainly milk and are they not unskilled? All they can do well is cry or dirty their diaper. They do that with the expertise of a master. But anything else, any other requirement of life, they can hardly do anything. What do they need? They need time. They need growth. They need the kind of food that will sustain and support and produce growth to take them to the place where they are adults. All the while they are growing up they are going through experiences and becoming more skilled, tried, tested, and proven.

Hebrews 5:12-14

So in order to be a full age and to be spiritually mature, God's way of life has to be lived. His commandments have to be used and exercised. The principles throughout the Bible, the precepts, the statutes, all have to be lived and used in order to discern both good and evil. There are people whose spiritual development has been slowed or halted. They stopped learning years ago, and their conduct is like that of a child. And yes, Jesus said the greatest thing in the world is a childlike spirit. But there is a substantial difference between a childlike spirit and a childish spirit.