Sometimes the Bible speaks hard words to shake us out of our complacency and to encourage us to advance spiritually. We find such words throughout the Prophetic Books, for example, in the many oracles calling the people of God to repent lest they face harsh discipline. The author of Hebrews, being a master rhetorician, uses hard words to shock his audience into action as well. In Hebrews 5:11–13, he essentially calls his original readers spiritual infants. They should have been ready for more substantive doctrine—spiritual solid food—but they still required spiritual milk.
The author of Hebrews will eventually give solid food consisting of more detailed instruction in the high priesthood of Christ (chs. 7–10), which means that 5:11–13 is a bit of an overstatement. But it is an overstatement designed to get the original readers to reassess their situation for the sake of their long-term spiritual well-being. In effect, the intent is to get the first readers of this epistle to think: “I really am behaving in a spiritually immature manner by seriously considering apostasy. I need to behave more like the spiritual adult that I truly am.” In reading this text, we are to challenge ourselves similarly. If we have been Christians long enough to have reached a degree of spiritual maturity, have we actually reached that maturity, or are we still spiritual infants?
Milk is needed for infants. For the first six months of their lives, babies can get all that they need for growth and health from their mothers’ milk. After that, milk becomes insufficient, and children must begin eating solid food to continue growing. So it is spiritually. Spiritual milk—the basic facts of the gospel and Christian practice (6:1–3)—is good. In fact, such milk should be a continual part of our diet for the rest of our lives (see, for example, 1 Peter 2:1–3). But we cannot live only on milk forever. We need additional spiritual nourishment that comes with spiritual solid food—instruction in the finer and more complex points of doctrine.
Such solid food, Hebrews 5:14 reveals, is for spiritual adults—more mature Christians who are continuing to grow into maturity. They are able to increasingly benefit from it as they are trained by it to “distinguish good from evil” with respect to ethics and to true doctrine versus heresy. Such people become able to differentiate not only between truth and outright falsehood but also between truth and half-truth.