Answer:
When God said "the least of my brothers", He's referring to the poor, the ones society rejected, the ones nobody cares for. God loves those who do selfless work, for it means they have no expectation of payment or appreciation. And in that selfless act of kindness, they are the most worthy to be by God's side in heaven.
Step-by-step explanation:
The lines given are from the book of Matthew 25:40 from the New Testament of the Holy Bible. The particular part of chapter 25 is a parable about heaven when the Son of Man will deal with the dead.
Subtitled as "The Sheep and the Goats", verse 31 to 46 tells what will happen to those believers who helped the least of the people. Unlike those (represented by the goats in this chapter) who attend only to the rich and to those they are sure of repayment, the sheep will be welcomed by God to sit in his right hand.
When God said "Truly I tell you, whatever you did for one of the least of these brothers and sisters of mine, you did for me" he is referring to those who do not hesitate to help anyone in need, irrespective of the person or social condition. They selflessly help others, without expecting anything in return. And that selfless sacrifice and help to the least of the people is greatest in the eyes of the Lord.