Discernment is a biblically informed judgment whether certain extra-biblical moral actions are good or evil. Last week, we looked at discernment in Eph 5:7-11 and pushed forward our argument that discernment is a crucial element of New Testament ethics. This argument is sound (and I am not the first to make it), and it is built on several passages, as we have to this point argued: Phil 1:9-11 (Part 1), Rom 12:1-2 (Part 2), Col 1:9-10 (Part 3), and 1 Thess 5:19-24 (Part 4). I have also argued that there are manifold implications from the sound and clear teaching of the Bible; more often than not, our problem is not having to go beyond what Scripture says to determine what is right and wrong, but not being informed to a great enough extent concerning the actual and binding implications of what God has already revealed concerning himself. As Kevin Bauder has argued, “we regularly employ second premise arguments in our moral reasoning.” Again, discernment or judgment is absolutely essential in this moral reasoning process.
This brings us to Hebrews 5:11-14, where the inspired author writes:
 About this we have much to say, and it is hard to explain, since you have become dull of hearing.  For though by this time you ought to be teachers, you need someone to teach you again the basic principles of the oracles of God. You need milk, not solid food,  for everyone who lives on milk is unskilled in the word of righteousness, since he is a child.  But solid food is for the mature, for those who have their powers of discernment trained by constant practice to distinguish good from evil.
Here the author of Hebrews pauses before launching into his great section concerning the Melchizedekian priesthood of Jesus Christ to address the immaturity in some of the Christians to whom he is writing. Though he has much to say, it is “hard to explain,” because the church is “dull of hearing.” They should already be teachers, but they have already forgotten the elementary teaching of the faith.
This immaturity is in part a “Word” problem. He stresses this in several ways: they should be teachers of the word of Christ; they need to be taught again the foundational principles oracles of God; they need milk because of their lack of skill in the word of righteousness. Frankly, the Hebrew Christians were immature because they did not know the Bible well enough.
But if the cause of their immaturity was a lack of knowledge of God’s Word, the evidence of their immaturity was in a lack of discernment. Here the author lays out the characteristic of a mature believer. They feed on “solid food,” having “their powers of discernment trained by constant practice to distinguish good from evil.”1 The word for “discernment” in this passage is different from the one used in other texts surveyed in this series, but the idea still is one of distinguishing by means of judgment.2
The point to stress in this passage is that this discernment is a mark of Christian maturity. Christian maturity means we are taking our knowledge of Christ and his word and all its instruction for us, and rigorously applying it to moral situations so that we can with judgment ascertain what is good and evil.3 To simply play the “Christian Liberty” card every time a moral question is raised is to surrender into the bunker of Christian immaturity. Jesus Christ has instructed us through his apostles that a sign of our maturity in the faith is the ability to discern good and evil.4
Discernment is even a sign of maturity for our own children. A child is immature when he only follows the letter of the law in a binding, legalistic way. When we tell him to clean his room, our children may take all their toys and shove them underneath their beds and to the corners of the room. This is immaturity. The floor is cleared, but the problem has been moved. A child is mature when they take their toys and put them away. We want to them to clean with discernment. We may tell our teenager son to sing during the worship service, and he may do so with only half-hearted vigor. And then he fails to pay attention to the Scripture reading or sermon. He may protest that he did what we asked of him, but this is immaturity. He in fact did not. He needs discernment, the ability to take our instruction and really apply it more extensively.
Turning back to Hebrews, this sign of maturity (discernment) is being constantly practiced or exercised.5 This is not an occasional call for us as believers, but one God is calling us to do constantly. This too is a theme we have returned to several times in this series–God is calling us to an active life of the mind in judging between good and evil in our age. This has far-reaching implications whereby we are constantly showing discernment in what we say, what we do, how we act, what we permit in entertainment choices, and how we worship. It is the baby who has every decision made for him. While we are to watch the example of pastors and other mature Christians around us (here too is a neglected truth of our age; 1 Thess 1:6; 2:14; Phil 3:17; Heb 13:7), we are not being told to simply fall in line with the status quo of the prevailing ethics of the particular Christian movement in which we find ourselves.6 We are being told that a mark of maturity is a constantly exercised discernment regarding good and evil in the world around us. This constant use is what trains us in greater discernment. By implication, the inverse would seemingly be true: letting this muscle of discernment go will lead to greater atrophy in discernment and we will become more and more immature.
So in Hebrews we have another call for us to put the Christian teaching we have received into constant exercise, discerning between good and evil. This ability is a mark of Christian maturity. Discernment is a biblically informed judgment whether certain extra-biblical moral actions are good or evil. Many evangelicals today want to duct-tape our mouths and shut down our minds when it comes to discernment and relegate seemingly every extra-biblical moral considerations to a matter indifferent. What we have seen, however, is that Scripture itself tells Christians to judge such moral questions and ascertain whether they are good or evil. In fact, if we neglect the constant exercise of such discernment, we are in a state of Christian atrophy and immaturity. The ability to discern between good and evil is a distinguishing mark of Christian maturity.