What is 帰す form here?

Question

The relevant bit goes like:

我が祈りを聞き給え

生きとし生けるものすべては主に帰せん

我が魂よ再び安らぐがよい主は報いて下さるがゆえに

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.

Answer 1

Yes, it's a mizenkei and the ん is a volitional auxiliary as you say. 帰す（きす） here stands for to be attributed to, and the conjugation goes きせ(ず) きし(たり) きす(べし) きする(こと) きすれ(ば) きせよ.