Violet tells Amos "the Lord's been mighty good to you, Amos, and I think he wants you to be good to yourself." What does Violet mean?

Violet is referring to the fact that Amos gives so much of himself, as well as his hard earned income to help others, that he puts himself into a precarious position. She isn't talking about his goodness here, she's talking about working himself to the bone to give money to people unwilling to work..... that he would do better to give work, and to pay for the work that is done.

While the words were strong within her she knew she must speak them. "With all the help the town gave her she never made herself any better," Violet insisted. "The children are getting older. They're the ones to help her and help themselves too. You'll do more for them all by giving work to the boys than by giving money to Lois."
"But Violet--"
She would not listen to him until she had had her say. "There's a fire that burns fast the more fuel goes on it and that's shiftlessness," Violet said stoutly. "Lois is a shiftless woman and money is just so much fuel to her fire."
"But Violet," he reasoned with her, "we've got good trade. The money comes in all the time and in another few years we'll be able to buy some land."
"A man has just so many years to live and he should have something that his heart is set on before he dies. The Lord's been mighty good to you, Amos, and I think He wants you to be good to yourself. Maybe that's why He let you buy me."