Simplify the following text for a Grade 11 native English-speaking person.
Original: Faust 's arrangement is that if during the time while Mephistopheles is serving Faust , Faust is so pleased with anything the devil gives him that he wants to stay in that moment forever , he will die that very moment ( in German he says : â Verweile doch , du bist so schÃ nâ â `` â Stay a while , you are so beautifulâ .
Simplified: Faust 's arrangement is that if during the time while Mephistopheles is serving Faust , Faust is so pleased with anything the devil gives him that he wants to stay in that moment forever , he will die in that instant .