I'm not sure I understand exactly why the absolute truth of the word of an omnipotent being (god) would need to be preached by anyone? Wouldn't such truth be self-evident to everyone, and as such need no one to preach it?

If god wants all humans to believe in him, why did he not simply make such knowledge inherent to/in us? Seems to me it would have saved a great deal of trouble...

If Jesus died on the cross for all our sins, then why are there still sinners? If you blame that on the devil, I remind you that (according to Christian faith) god created all things, including the devil.