My philosophy teacher doesn't believe in God at all. He is still young and therefore has the chance to go back and repent. Is it my duty to talk to him and try to convince him to believe in God fulfilling our Lord’s command that we should go and preach to the whole world?
It is our duty to reach every person and spread the word of God at all times and on every occasion. If you have the chance to evangelize to your teacher then do it without hesitation; for we know that God "Desires all men to be saved and to come to the knowledge of the truth" (1 Tim 2:4).