He supported it because he believed that the powers enumerated in it balance each other out and nobody could become tyrannical by exploiting it. He refers to it as an open door because it can be amended meaning that if something needs to be changed because the spirit of the time has changed, it can be done while keeping the good things.
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IDK if i am right but i would say the puritans as they wanted to get rid of the catholic rituals because they wanted to be pure. hope i helped tho
Answer: An ecumenical council is a conference of ecclesiastical dignitaries and theological experts convened to discuss and settle matters of Church doctrine and practice in which those entitled to vote are convoked from the whole world and which secures the approbation of the whole Church.