For everyone who partakes only of milk is unskilled in the word of righteousness, for he is a babe. But solid food belongs to those who are of full age, that is, those who by reason of use have their senses exercised to discern both good and evil.

Hebrew 5:13-14 (NKJV)

A spiritual baby is a person who is untrained in the word of righteousness, or the gospel of God's grace. "Unskilled" is apeiros in Greek, which means "inexperienced or ignorant" (Strong's G552). In this sense, spiritual development and growth involve constantly learning and applying the truth of the gospel in your daily life.

According to the Apostle Paul, our "mastery" of the gospel enables us to discern both good and evil. Diakrisis is a Greek word that means "distinguishing, judging" (Strong's G1253). It is the God-given ability to make decisions about our lives and directions based on gospel truth rather than hearsay or personal biases.

Discernment functions as a filter through which we decide what we let in and what we let go of in our lives. This means that when we examine or evaluate our attitudes, habits, and values in light of the gospel, the truth or falsity of what we believe will be clearly revealed and understood by who and what we have in Christ. In other words, discernment is the key to living the abundant life in Christ.

A lack of discernment fractures the soul.

The person who lacks discernment is always unhappy, always guilty, and always wanting to give up.

Discernment is the result of intimate knowledge of the gospel. When you feed on "solid food," or the rich truths of the gospel, you are not only finding your identity in Christ, but you are also aligning your senses—spiritual intuition, intellectual faculty, and emotional feelings—with Christ. When your mind and heart fully resonate with the gospel, you become sound in all aspects of your life. Then you are no longer driven by impulses or stifled by self-sabotaging habits, but capable of distinguishing between good and evil. This is a sign of spiritual maturity.