This community is not in communion with the Catholic Church so I guess they can do what they want. I think it is possible for Muslims to worship at a Catholic Christmas Mass as long as they don’t receive Communion.
I find no problem with this. You do not have to be a believer to attend church. All are welcome. If we do not welcome other people into our churches how can we hope to give them the Good News?
Obviously, in a Catholic church the Muslims, or other non-Catholics, could not be admitted to Communion. I do not think even the most liberal Anglicans/Episcopalians would admit Muslims to ‘communion’.
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