Looking at things from a higher level, we live in a body for awhile, then discard it, only to take on or inhabit another body again when the time is right. We do this over and over for the purpose of experiencing all that we can. We get ourselves into tight places, and then find our way out. We are the good guys until that gets boring enough, then we are the bad guys until we learn our lessons there. And on and on it goes.
When we are able to see the larger picture, we discover that we are incarnating into body after body, lifetime after lifetime, and from this perspective, we leave a legacy to ourselves. When we do something to make this world a better place for our children or for future generations, we are really making it a better place for ourselves. Indeed, we are the ones who come back, time and time again, to harvest the fruits of our own labors.
That's one point of view. Here's another.
At Its purest Essence, the Being, or Entity, or Spirit (or whatever you'd like to call It) that resides inside your body is the same Spirit that resides in everybody else's body. Outwardly, we have different identities, different preferences, different physical characteristics, different formative programming, different cultural influences, different astrological configurations, different genetics, different strengths and weaknesses, different you name it, but one thing we all have in common is the core template we start out with. At the center of our Beings, we are the same, and in some mysterious way, a connection, which is typically kept hidden from us, exists between the Being inside our body and the Beings inside every other body we see. Just as one drop of water is part of the whole ocean, so is one person's Spirit part of a much larger, vaster, collective Spirit that is made up of all Spirits. When our differences are put aside, and our connections to each other are brought to light, we see ourself in everyone else. We know that we are One, and that the good works we leave as a legacy for others is really a legacy we are leaving to ourself.