In this answer Palatino text font is used together with the AMS Euler (eulervm) math font. The following statement is reasonable:
Note also that because the "Euler" fonts have an upright rather than slanted appearance, the text part of the Residue Theorem's statement is set in upright letters rather than in italics.
If the Theorem's statement is set in upright letters, what is the best/correct way to mark the end of the Theorem and the beginning of "normal" text?
ntheorem, which is the package I know best. Also, these theorem structures have a special vertical spacing built-in, which you may increase. – Bernard Jun 18 '14 at 20:06