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I have visited a number of churches all over the world over the years and all have welcomed me to take part in Communion, the only exception being the Catholic Church.
I was in the line for Communion when an usher gently took hold of my arm and quietly asked me to return to my seat. They had gone and questioned my host, who freely admitted I was a Protestant 'elder'. I was ushered back to my seat and told to stay there.
In my opinion a non-Catholic should not take Communion at a Catholic church; because if you think about the institution of the last supper in Luke 22:19, it is meant to be shared among believers who are of the same heart and mind as yourself. Just the name Communion is self explanatory, the church must be in communion and in unity with all of its members, of the same belief; otherwise it will not stand.
During a Catholic Communion, when you queue to receive the bread, the minister will raise the consecrated bread in front of your eyes, and declare, "This is the body of Christ."
At this point, a response is needed. Would you agree and exclaim, "AMEN!" or would you disagree and say, "No, that is simply bread."
A third option is possible, though I do not recommend it. To pretend to believe and say "AMEN", yet deep inside his heart disagree.