What did the lawyer learn about life?

The lawyer learned that imprisonment was in fact more humane that the death penalty, in that the prisoner was given the chance to study, meditate, and improve his character. He proved that rehabilitation is possible. 

"I don't agree with you. . . . I have not tried either the death penalry or imprisonment for life, but if one may judge a priori, the death penalty is more moral and more humane than imprisonment for life."