I'm not religious, but if you are, then look at it this way

The ones that have passed away, have done all they were suppose to on this planet.If someone is left alive, regardless of how much people care or not, it's because that person is given another chance.Another chance to make himself a better person, to live a good life and hopefully to find peace.

Use the chances you can get, and don't take life for granted.Be happy for what you have, how ever small it may be.