"With those" refers to people or things who are closest to the One being most perfect. You could also say "those who are closest..." when officially referring to people. In other words, the sentence is trying to say the people or things who are the closest to the One are the closest to perfect, while the people or things furthest away from the One are the least perfect. In this sentence, I would say the use of "with those" serves as a comparison of two opposing sides, one of those being the result of being closer with the One, and the other being further away from the One. The only thing I would say is missing from this sentence is the word "a" in between is and pure. I would personally say "the One is a pure being..." because it is a necessary article to use to address whether you are speaking about a specific person or thing or a general one. I hope that helps!