After issuing his call for Christian maturity, the writer to the Hebrews explains his idea of Christian maturity in terms of food. These Hebrew Christians, he says, need milk because they are unable to handle “strong meat.” The analogy is evident: babies eat milk because that is all their digestive system is able to handle. If you give a baby steak, it will cause all sorts of problems. The same is true of young Christians: they need to be spiritually nourished with simple and easy things from the Scriptures. If the first spiritual food a new Christian tastes is a lecture on historical-grammatical exegesis, for instance, it will likely do them more harm than good.
The problem works the other way too, though. An eight-year-old that only wants milk for supper has as big a problem as the steak-eating newborn. In time, it is necessary for children to stop eating pablum and move on to vegetables, cereals, and meats in order to grow to physical maturity. The same is true of the Christian life. It is very proper for a new Christian to spend time learning the “first principles” of God’s Word. In fact, it is very necessary. Nevertheless, their diet must eventually expand if they are to continue growing.
The author’s idea of Christian immaturity, then, is very straightforward. A “baby Christian” is someone who is “unskilful in the word of righteousness” (5:14). He doesn’t know all the Bible stories, he isn’t familiar with all the important doctrines of God and salvation, and he doesn’t see how all the instructions in the Bible apply to him. No matter how intelligent, experienced, sane, or informed a Christian individual may be, he is an immature Christian until he is skilful in these matters.
So we see that Christian maturity consists in being skilful in using the Scriptures. What, then, does this skill look like? The author tells us more in the following verse (5:15): mature Christians, he says, are “those who by reason of use have their senses exercised to discern both good and evil.” That is to say, their minds have been trained through practice to recognize right and wrong.
There are three elements, then, that comprise Christian maturity. First, Christian maturity requires a knowledge of the Bible. The author evidently intends to say as much, for by what other standard are to identify “good and evil“? We must know what the Bible says is right, and what it identifies as wrong.
Second, Christian maturity requires biblical discernment. It is not enough to know “good” and “evil” as they appear in the Scriptures. We must also be able to identify, based on the Bible’s teaching, “good” and “evil” in our own lives and circumstances. Knowing the commandment, “Thou shalt not bear false witness,” is one thing; being able to recognize deception in the world around us and in our own hearts is another.
Third, Christian maturity requires sustained effort. The author uses the phrase “by reason of use” and the word “exercised” to remind us of this fact. Biblical knowledge and biblical discernment don’t drop from the sky. They are to be acquired progressively by constant spiritual effort and exercise.