Beginning today, treat everyone you meet as if they were going to be dead by midnight. Extend to them all the care, kindness and understanding you can muster, and do it with no thought of any reward. Your life will never be the same again.

This quote is suggesting that you should treat everyone you meet with respect and kindness. Act as if you are aware that they may not be here in the world by the end of the day. Do not expect anything in return; just offer your care, kindness, and understanding to them freely. If you follow this advice, it is likely that your outlook on life and relationships with others will improve significantly.