His perspective on love (in The Road Less Traveled) is that love is not a feeling, it is an activity and an investment. He defines love as, "The will to extend one's self for the purpose of nurturing one's own or another's spiritual growth." Love is primarily actions towards nurturing the spiritual growth of another. Love cannot be sustained by mutual dependence; rather, love between two parties is made stronger when they are completely independent of one another.^[1]

Peck seeks to differentiate between love and cathexis. Cathexis is what explains attractions to the opposite sex, the instinct for cuddling pets and pinching babies' cheeks. However, cathexis is not love. All the same, true love cannot begin in isolation, a certain amount of cathexis is necessary to get sufficiently close to be able to truly love.

Once through the cathexis stage, the work of love begins. It is not a feeling. It consists of what you do for another person. As Peck says in The Road Less Traveled, "Love is as love does." It is about giving the other person what they need to grow. It is about truly knowing and understanding them.