Numpad 1: God Mode - toggle on while you are in the game and most
things cannot kill you.
in the game means, actually in the game, playing, with the character running around in the world. Note it also says MOST things will not kill you.
Hmm strange that been a high level can skip missions sounds like a bad game design to me like if you decide to do all the things in the area and go up in a level you might miss out on missions is pretty dumb.
Oh so it does makes the missions the same level as you are well that is not to bad seeing as how I'm mostly doing stealth kills