Indy Opening Line ?

Indy Opening Line ? Can someone shed a little info on why the Indy opening line was 4 and is now 3'? Indy last two games: 34-17 over seattle and 31-10 over ARI Tenn last two games: 17-37 loss to Jac and 17-24 loss to NYJ What am I missing here? Would really appreciate feedback. I am trying to learn and this makes no sense to me...