So that you cannot say, "I had no idea."
"For I was hungry and you gave me food, I was thirsty and you gave me drink, I was a stranger and you welcomed me, I was naked and you clothed me, I was sick and you visited me, I was in prison and you came to me.’ Then the righteous will answer him, saying, ‘Lord, when did we see you hungry and feed you, or thirsty and give you drink? And when did we see you a stranger and welcome you, or naked and clothe you? And when did we see you sick or in prison and visit you?’ And the King will answer them, Truly, I say to you, as you did it to one of the least of these my brothers, you did it to me."
Its not the big things, but rather the random acts of kindness that make the difference.