Priest asked me to change or leave

[Corki]

He is not going against the missal. I am glad you’ve read the whole GIRM… now read the whole missal. I’ll save you the trip

“[The posture of the people during the Eucharistic Prayer is different in various countries and regions; in the United States, the people normally stand until the “Holy, Holy”, and then kneel until after the “Great Amen.”]”

There is nothing authoritative in this verbage. This in no way sounds like direction but rather guidance. Keep in mind I would kneel, even in his situation, because as it was pointed out… uniformity does not preclude one from kneeling if he chooses to do so.

But lets be clear, the priest having everybody stand is not in conflict with the Missal, it just fails to take the Missals suggestions.

It doesn’t matter if the verbiage in the Missal is authoritative. That’s what the GIRM is for. The entire GIRM is instructional/directive. There are some places where there are suggestions but most of the GIRM is directive. The places where there is an option available are clearly noted. If the GIRM says to kneel, even after the US adaptations are taken into account, to direct the congregation to stand without a good reason (also as indicated in the GIRM) would be to direct them to go against the Missal.