This is a play on words of sharpening your pencils when you are in school. When you are going to write an exam, its like going to war. Your pencils are your army, which is also a play on words as a army is used in war. The saying says that you need to sharpen (educate) your soldiers on war, and the consequences of it. The pencils aren’t comepletly straight to emphasise that even in an army people have their faults and it might look perfect from the outside.