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speratus said:
The words of institution should be repeated because Christ says, "This do."

But neither He nor any of the apostles ever said, "This repeat." They never said that Paul's words from 1 Corinthians 11 were to be stated as "words of institution" over the Lord's Supper. You might think that it is a good idea to do so, but you cannot bind others to do so.



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speratus said:
The validity of a sacrament does not depend on the person administering the sacrament but upon the words that are spoken and the promises attached to those words in scripture.

The promises and admonitions attached to the practice of the Lord's Supper should be made known to those who are partaking of it. But it is not scriptural to maintain that there must be some set formula ("words of institution") that must be spoken in order to make the sacrament valid.



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speratus said:
However, scripture also teaches that ministers should administer the sacraments.

What is your definition of a minister, as you are using it in this sentence?