Paul tells us clearly:
Rom 1:16 For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek.
Rom 1:17 For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith.
This is the gospel of Christ. To be preached and lived out.
Make makes a number of points as to why this is so offensive to the world.
Rainbow Trout 