Christianity starts with the assertion that there is something deeply wrong with the world. It starts with the observation that the world is not as it should be and the conviction that what is wrong is not some minor flaw that can be easily removed by just a bit more human effort. Christianity tells the story of the world as the Bible does: It is a good creation that is fallen.
If you do not accept that story, then there is little in Christianity that makes sense. If you think the world is basically good and getting better all the time, then it does not need a savior and we do not need Jesus. If you think that the only problem in the world is that we have not yet tried hard enough or discovered the right tools, then you will not believe that the solution to every problem has already been given to us.
Christians tell the story this way. God created all that is and gave us dominion within his good creation. And God gave us the free choice to live in harmony with and obedience to his just, perfect, and loving commands. We rejected these gifts. We broke the world. We ushered in death and all the evils that follow in its train. And as the world shattered, we were shattered down to the very deepest depths of our heart and soul.
Salvation is nothing less than a restoration — a recreation — in the life of a person and the entire world of the joy, peace, harmony, and love that God first instilled in us. It is a gift and work of God, but one we must both accept and nurture within ourselves, for the old impulses die hard.
A preacher named John Wesley believed this and taught it to anyone who would receive it. As United Methodists — but I would argue as Christians — this is what we teach as well.