I think that Steinbeck focuses deeply on the atmosphere of the last chapter. First of all he goes back to where he starts the novel, before any bad things happened to the two friends when they were happy and still with dreams of a better life. He first makes George reassure Lennie and make him feel as if he was in heaven; all the things they wanted then he shoots him. George reassured him with words like “I ain’t mad. I never been mad, an’ I ain’t mad now. That’s a thing I want ya to know.” George inspirits him before his death.
If Lennie was going to be killed by a man of the ranch he would had suffered more and would had died in pain and even if George would had helped him escape like in Weed they couldn’t had kept running from things for the rest of their lives. The second option for Lennie was to go to jail and risk the electric chair. George had to do it for everybody’s sake because Lennie could had done the same thing again, then slim said to the Suffering George “Never you mind…A guy got to sometimes”
Lennie not being very bright likes to stroke live creatures and at all times he kills them. Maybe George exaggerated his action of killing his own friend and partner of “job migration”. The incentive is that George, even if he killed him while he was at peace, he promised aunt Clara that he would have take care of him, I think that killing is not a good way of taking care of a person. I can’t decide whether he made the right choice because I’m not the writer and I can’t change things; although I personally remain of the Idea that only and only God can decide of the faith of any human being, this is my idea even though George made him die in peace.