I was asked this question while discussing a passage from the Epistle to the Hebrews, in which the Apostle Paul writes:

“By this time you ought to be teachers, yet you need someone to teach you the elementary truths of God’s word all over again. You need milk, not solid food.”

And indeed, how can we tell?

It would clearly be misleading to measure spiritual maturity simply by the amount of time someone has spent within the Church. A person may attend services for decades, know the order of worship by heart and be well versed in religious texts, yet remain spiritually immature. Someone else may only recently have come to Christ, and yet there may already be a certain depth in the way they see the world and treat other people.

When we speak about growing up, we usually turn to psychology. Psychological maturity is often associated with the ability to take responsibility for one’s life, regulate emotions, make conscious decisions, accept criticism, resolve conflicts constructively and become less dependent on the opinions of others.

All of these things matter. Christianity does not somehow cancel ordinary human maturity.

And yet spiritual growth seems to be about something more.

The Apostle Paul offers a particularly striking criterion for spiritual maturity: the training of our senses to distinguish good from evil.

I find this thought especially compelling because Paul is not talking simply about the amount of knowledge we possess. He is talking about an inner vision—a way of seeing.

Distinguishing good from evil is not nearly as simple as it seems when we are children. As children, the world often appears straightforward: these are the good people, those are the bad ones; this is good, that is evil.

But the longer we live, the more often we encounter situations in which everything becomes mixed together.

We can do the right thing outwardly while being motivated inwardly by vanity or the desire to prove ourselves. We can speak about truth while using our “truth” to wound another person. We can fight for justice and, somewhere along the way, become hardened ourselves.

This is where Paul’s idea of the “training of our senses” becomes so important.

It is not merely about knowing the commandments. It is about developing the ability to recognize, in our hearts, what is actually happening—to us and to the person standing before us.

Perhaps a spiritually mature person is not someone who never makes mistakes. Rather, it is someone who becomes increasingly attentive to goodness.

Someone who begins to notice irritation, pride or the desire to humiliate another person a little earlier than before.

Someone who learns to recognize the difference between what is motivated by love and what merely resembles love from the outside.

This may be why spiritual growth is so difficult to measure. It does not necessarily announce itself through knowledge, achievements or years spent in the Church.

Instead, it reveals itself in small things: in a pause before we respond in anger, in the ability to admit that we were wrong, in forgiveness, in compassion, in the growing awareness of what is happening inside our own hearts.

And perhaps this is one of the signs of genuine spiritual maturity: not that we become certain that we already know the difference between good and evil, but that we become humble and attentive enough to keep learning how to recognize it.

Because the deeper we look into the human heart, the more complex it becomes—and the more carefully we must learn to see.