。
Resisting temptation is hard.
Literal
Temptation [to-に] resist-[nominal-こと] [topic-は] difficult.
抵抗する ('to resist') is a suru-verb taking an に-marked target — things one resists are marked with に in Japanese. ことは nominalizes the verb phrase so it can serve as a topic. 難しい ('difficult') is the standard assessment. A neat textbook example of こと-nominalization.