Matthew 25:45
Then he will answer them, saying: truly, I say to you, as you did not do it to one of the least of these, you did not do it to me. The identification applied negatively: the failure to serve the least of these is the failure to serve the King. The indifference to human need is indifference to the Son of Man who identified himself with those in need. The as you did not do it to one of the least of these mirrors the as you did it in verse 40: both the mercy and the indifference are received by the King himself.