The twentieth portion of Torah is largely focussed on how Aaron and his sons (the High Priest and Priests respectively) should be prepared for their roles. These instructions are wide-ranging, covering clothing and ornamentation, posture and attitude, and ritual ceremonies required to bring about the appropriate decorum and religious connection to the Divine. Along the way the passage does also dive into the complex and somewhat troubling  practices of ritual slaughter, an idea that has become not just outmoded in our time, but is seen with more than a little concern for animal rights and for what we now believe is the core nature of our relationship with G-d. In this, it is essential to remember that Torah is written in a period that vastly predates our modern age, and as such represents the understandings and worldview of a very different time.