Matthew 25:31-46 is a little too long to reprint here. You'll have to read it yourself. But let me paraphrase.
On the day of judgement Jesus will separate people to His right and to His left.
He will say to those on His right, “Come, you that are blessed by my Father, inherit the kingdom prepared for you from the foundation of the world; for I was hungry and you gave me food, I was thirsty and you gave me something to drink, I was a stranger and you welcomed me, I was naked and you gave me clothing, I was sick and you took care of me, I was in prison and you visited me.”
They will ask Him when did they do these things. And He will respond "Whatever you did for the least amongst you; you did it for Me!"
Then He will say to those on the left, "You that are accursed, depart from me into the eternal fire prepared for the devil and his angels ... ... ..."
They saw similar people in their lives and ignored them and did nothing to help.
Could it be clearer than that?