Let's say we can consider spiritual growth to be evolution on an individual level. Through out the course of our lives we have the capacity to grow and evolve from an immature, self-centered child to a loving, caring and emotionally mature adult. The fact we achieve spiritual growth at all in itself is amazing, considering all the difficulties and suffering people have to endure in their lives.

In order to understand spiritual growth from another perspective, let us venture into the world of physics for a moment. Physicists have developed what is called the Second Law of Thermodynamics, also known as the law of entropy. It is the formal explanation for the natural tendency for physical objects to break down, wear out, and degenerate. This law states that the amount of disorder in a closed system always tends to increase, and will never decrease. 

For example, ice cubes in glass of hot water will always melt and result in lukewarm water. The ice cubes and the glass of hot water have more order, and therefore less entropy than a glass of lukewarm water. The glass of lukewarm water has more entropy because its contents have a uniform, undifferentiated temperature. According to the Second Law of Thermodynamics, development and growth of a closed system do not happen automatically; outside influence, or input in the form of energy, direction, or control, from outside the system is required.

The same is true in our spiritual growth. Our natural inclination is to take the easy way, to coast down towards a state of maximum spiritual entropy, to not challenge our understanding of reality, and to not expand and push out our limitations. It takes effort, and does not just happen by itself. But as we all know, people do grow and develop spiritually, in spite of the opposing force of spiritual entropyt

So what is "outside influence" that empowers us to go against the downward spiritual tide in our lives and to make the effort required to grow and develop? It is none other than the power of love. It is through our effort to love others and to receive their love, and to extend ourselves for the sake of the spiritual growth of our fellow human beings that we can overcome our own spiritual stagnation. With the power of love we can also overcome laziness, fear, and self-centeredness. Loving others is the key to accomplishing spiritual growth. This is the main point of The Road Less Traveled.

The most outstanding capacity we have as humans is the ability to love and sacrifice ourselves for other people. The greatest saints and sages that ever lived were all known for their love, compassion, and sacrifice for mankind. Even though we cannot all become like Mother Theresa, if this is in fact the highest calling in life, then learning to love others is of paramount importance.