The relevant bit goes like:
Going off context ん seems to be a volitional auxiliary (推量) as it would make the middle bit as "to you (the Lord) all living beings shall come". Is it that or something else?
But how does 帰す conjugate here? Is 帰せ an older mizenkei?
Edit: I've found some examples, such as
乙女のすがたしばしとどめん I want to keep the image of the young women for a while.
However, I don't know if this verb is the same as modern とどめる, which wouldn't make much sense attaching 連用形 to volitional. If とどめ were a mizenkei form of some other verb it would start making some sense to me, I think.