In chapter 10 of Goethe's Faust, Gretchen brushes off Faust. Faust wants Mephistopheles to help him, since Gretchen is above 14, but Mephistopheles declines. Then Faust says
Mein Herr Magister Lobesan,
Laß Er mich mit dem Gesetz in Frieden!
It seems that he calls Mephistopheles "Herr Magister Lobesan" and it may have something to do with law.
Who is "Herr Magister Lobesan" or what does it mean?
"lobesan" is an outdated word from Middle High German that means something like "commendable", "laudable" or "pious". It was already outdated in the 16. century. "Magister Lobesan", also found as "Meister Löblich" or similar, is an tongue-in-cheeck reference to a pendantic scholar with an undercurrent of mustiness.
Faust basically pokes fun at Mephisto because the devil, of all people, warns against breaking the law. You could translate it as something like "Oh please, Master Righteous, leave me alone with the law!"
The word is properly «lobesam». The meaning is the one that Henning has explained. It has the same ending -sam that is also found in words such as einsam, seltsam, gehorsam, etc. Goethe uses the form «lobesan» with a final -n instead of -m so it forms a rhyme with the preceding «an»:
Mephistopheles: Geht aber doch nicht immer an.
Faust: Mein Herr Magister Lobesan,
The reason why the word can have an -n instead of the -m might have to do with final nasals being dropped altogether in Goethe’s Frankfort pronunciation, as can be seen in other rhyme pairs like the following:
Es war einmal ein König,
Der hatt’ einen grossen Floh,
Den liebt’ er gar nicht wenig
Als wie seinen eignen Sohn.
