Use of particle に


What is the reason why に is used in this sentence instead of が or を?

> 外国語を使って仕事をしていらっしゃる方々 **に** お集まりいただきました。

Does this いただく here stand for honorific of する or of もらう?




I think it's from もらう here. 〜に〜してもらう is used to express that you "receive the
action from someone". They do it for you and に is the marker for the person
doing it.

いただく makes it humble, so you express that it's something like a favor for you.

お集まり is the honorific version of 集まる. As you are using いただく afterwards, you
don't need the する anymore. It seems almost like a nominalization to me.

The whole sentence sounds like "We have assembled people here who are working
in a foreign language", literally "We humbly received (the favor of)
assembling from people who are working in a foreign language".

