sarcastic - witty in a way which conveys scorn, irony, and/or insults. chain-smoking - smoking a lot of cigarettes. professor - teacher, usually at university level. challenged his students - he required work from his students which was demanding and stimulating inspired them - he stimulated their minds and ambitions M.Rabotin was man who is witty in a way which conveys scorn, irony, or insults, and smokes a lot of cigarettes. He teaches at the university level, and required his students to perform difficult work, stimulating their minds and ambitions. He did this by his strong interest in the subject he was teaching.

Short: M.Rabotin is a good teacher, professor and he smokes.

It means exactly what it says.

May be a typo? Remove the word "yet." The challenge was the inspiration.