What does it mean to act selflessly?
That you are to sever identification with the various roles you play in life. It is the student who studies, the spouse who supports his family, the human that eats, breathes, sleeps, etc. But you are none of these. You are merely the witness, the overriding consciousness associated with a certain body and mind that thinks certain thoughts and moves through life performing various actions. So you are spirit.
But what of this body, what of this role you play? Who is controlling it? Certainly not you, since you are merely the witness. God? But God is omnipresent, so you are God. A force/energy/presence? Merely another name for God. Let's not get lost in the semantics. What this notion of doership brings up is the concept of free will versus determinism.
Determinists like Chapman Cohen would say that "if we knew the quality and inclination of all the forces bearing upon human nature, in the same way that we know the forces determining the motions of the planet, then the forecasting of conduct would become a mere problem in moral mathematics." In other words, where you begin in life - who you were born to, what genes you carry, the time in which you were born - determines the next stage of life, which determines the next, and each action and thought is like a domino setting in motion the next.
Strangely this fact is not at odds with the notion of free will. What most people believe when they assert, "I am free," is that they are under no external compulsion to act a certain way. You are free to do something you wish to do, and not made to do said thing by someone holding a gun to your head.
But if your wishes are determined by your environment and upbringing, is that really freedom? Does the person who has never been exposed to ice cream, never seen, tasted or even heard of the dessert, get a craving to have a hot fudge sundae? No. He is not free to have a hot fudge sundae in that this is not an available option in his life; but if moves to a neighborhood with McDonald's and tastes a bite and wishes to enjoy a whole dessert for himself, he can do so, since "it is a free country" after all. Provided of course he has two dollars.
So the concept of one's not being the doer has a deeper significance. Not only are you not the body and mind that goes about daily life, but rather the witnessing consciousness merely along for the ride; moreover, even this body and mind are not the doers, in that they are under compulsion to think and act not by some external force but by the preferences they have developed over the course of their experience, modified by personality and genes. So there is no doer. At the level of the body and mind, we can say that there is doing. But at the level of spirit, there is only being.
So Vince Vaughn had it right when he said: "Be there." Of course he was talking to his car (in Dodgeball) but applied to one's own life it makes really good advice.