Wisdom traditions invite us to explore the idea that we are more than we seem to be. The personality we identify as "me" is a dynamic process rather than a fixed object; a verb as opposed to a noun.
Those who are of the world dedicate their lives to the pursuit of material things and to reinforcing the idea that the ego is the center of everything. To them there is nothing else.
Those who are in the world but not of it have a different focus. They believe that there is something beyond the ego, an essence that is far more permanent than the individual ego. This essence is referred to in wisdom traditions as Buddha nature, soul, and conscious awareness, among other terms.
Essence is the intrinsic nature or indispensable quality of something that determines its character. The something, in this case the ego, is an often distorted reflection of its essence. One who is not of the world seeks to find essence and in this search breaks down the structures, beliefs and pursuits that have defined him/her. He lets essence appear by dropping the veils that keep it hidden. As she does so a glow of clarity, happiness and compassion surrounds her.
There is no need to leave the material world and become a monk or hermit yogi. You can continue to do what you have been doing, your career, your family life, etc., all the time remembering that your ego personality is a reflection of essence; that your deepest aspiration is to actualize that part of yourself. Everything you do is directed towards that goal.
There is no need to drop out. You tune in and live life in the world, acting with the intention to let go of anything that keeps you from realizing essence. You excel in what you do, experience less unnecessary stress, and become healthier in your relationships. This is what it means to be in the world but not of it.
This, of course, is easier said than done. You may be in a situation in which those around you are only of the world. Speak to them about essence and you may be faced with ridicule, pity or concern for your mental health. Your own resolve may be shaky; based on a brief experience of essence. You might find that breaking down the beliefs and structures that have defined you as an individual in the world is frightening. Depending on what you have been doing in your life you might be changing outwardly and that might disturb family and friends. Relationships may change.
Resistance from those around you and conflicts with conventional thinking create confusion. Confusion leads to doubt and denial. At the same time, your experience of essence remains with you. It expresses itself as a subtle dissatisfaction. You may try to bury it in work achievements or in seeking fame or the perfect relationship. No matter what you do you cannot really deny it.
But once you acknowledge it, the rest of your life becomes simple.
You seek out teachers, techniques and teachings from wisdom traditions. You find others who are not of the world, while you guard against being drawn into false beliefs and distorted views. You build confidence in yourself and honor your experience of essence.
You live in the world while devoting everything you do to get to a deeper understanding of yourself with the ultimate goal of identifying with your essence.