Why do so many professing Christians say that salvation is an offer, when God says it's a gift?

I just answered a similar question that I think was you who asked. But for the sake of those who didn't read it, here goes. Let's say everyone in the world has aids and there is no cure. But someone comes up with the cure and is not interested in money but rather in helping people get rid of aids. This person offers the vaccine that will cure aids and commissions people to go spread the news saying: go into the world and spread the glad news; he that believes and is innoculated will be saved. He that doesn't believe will die. It is a gift and you would have to have faith that the innoculation would work whether you ever met your benefactor or not. Hope this helps.