It is interesting and quite revealing to know why also. This is during the times of Diaspora, and makes up what are known as the laws of separation. Obviously for a people dispersed with no land to keep it's people, language and culture together, these laws were motivated from a desire to keep people distinct an separate. In the following chapter of Leviticus you will find the command for a man not to cut the hair on the corners and sides of his face. This was again to keep that identity separate and alive so as not to be mistaken for a clean shaven Egyptian back then and a Roman later on. It is why Orthodox Jews still maintain side locks (peyos).
This sense of separateness can also be seen in Isreal's concept of holiness. This is not a sense of holiness that emerges from fear of displeasing a punishing deity, it is one derived from the Justice that deities own holiness personifies. This is where democracy comes from. A concern for the people not the object of devotion.
First to understand this, a misunderstanding needs to be erased. Israel, the Hebrew prophets and Judaism are not the same thing.
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