反而 is used when expressing something contradicting with the latter exceeding the expectation of the former statement. Take the sentence you have shared for example, it means that "He did not accept such a good offer but he quitted the job instead". Few more example for the usage of this word will be like "他并没有找到女朋友反而找到了男朋友" (He did not found a girlfriend but he found a boyfriend instead) or "他并没有找到他的钱包反而也把电话也弄丢了" (He did not found his missing wallet but he lost his phone instead)

他没有He did not 接受 accept 那份优厚的待遇 that rich offer 反而, on the contrary, 辞职了 he resigned.

楼上举的例子真是十分生动。。。。 The sentence "他没有接受那份优厚的待遇，反而辞职了” = "He didn't accept the liberal/excellent pay, instead, he quit. " 反而 = instead; on the contrary(go beyond expectations) In the sentence, apparently it's a surprising decision this person has made. So used "反而”

Adverb, meaning on the contrary; instead The sentence can be translated as: Instead of taking/accepting that good offer, he resigned. He did not take/accept that good offer. On the contrary, he resigned. Reference: Pleco (application). I highly recommend this app for foreigners who are studying Chinese.

反而 means exceeding one's expectations .People are all surprised at what he did and don't understand why he did so. At the moment,you can use 反而.