An oil lamp becomes brighter after trimming, a truth becomes clearer after being discussed.

解释 ( paraphrase )
油灯不时常拨动就明亮，道理不经过辩论就不能分清是非。过去用的油灯，燃烧一段时间后，需要把灯芯上烧成灰烬的灯花拨掉，灯光才会重新明亮。
这条谚语告诉我们：对于一个复杂的问题，只有通过不同意见的讨论和争论，最后才能弄明白，得出正确的结论。 

In the past, after an oil lamp had burned for some time it had to be trimmed; otherwise the light would grow dimmer.
This proverb tells us that facing a complicated problem, only by discussion and debate can we get the correct answer. Truth develops through the comparison of ideas. 

造句 ( example )
灯不拨不亮，理不辩不明，任何事情都要经过一番探讨才能深刻理解。