Where is the most concrete exposition on the Buddhist ethics in the source material?

In the Bible a complex saga of the human experience is elaborated in a multitude of ways, and these nuances make the text hard to crack in a linear reading. However, there exists a very illuminating chapter (Sermon on the Mount) that provides a very well articulated elaboration on what could be considered the core Christian ethics. It ultimately grounds the metaphysical landscape or at least informs many passages (both before and after it) to be more easily interpretted. I am interested in learning if there are any similar passages that could be pointed out in the Buddhist texts. My entirety of exposure to Buddhist source text currently is the Zen sutra on the lotus flower, and this question is open to any sect.