This verse speeks to me about how were not here to convince people that Jesus has risen but to tell them he has risen, we have no power over the decision they make or if they even beleive us. I know I get hung up on that sometimes. Jesus said if they don't have you dust off your feet and leave. Here in Proverbs it pretty clear that God is telling us not to argue with people who don't beleave. Being a witness is letting the world witness God threw us.