How can I change someone's mind on how she views the Lord's Supper?
I have a relative who said she believes taking the Lord's Supper looks like cannibalism. How can I change her mind about that?
I don't know if I can help. In order to have a discussion with anyone, there must be a commonality of language. Your relative refuses to acknowledge figurative language.
The Lord's Supper consists of unleavened bread and fruit of the vine. Neither of these elements is a physical part of any human body. Therefore there is no literal consumption of another person's body -- there is no cannibalism.
"While they were eating, Jesus took some bread, and after a blessing, He broke it and gave it to the disciples, and said, 'Take, eat; this is My body.' And when He had taken a cup and given thanks, He gave it to them, saying, 'Drink from it, all of you; for this is My blood of the covenant, which is poured out for many for forgiveness of sins'" (Matthew 26:26-28).
Since Jesus handed the disciples bread and said, "this is my body," it is clear that Jesus is using figurative language -- in particular it is a metaphor. A simile will mildly state that one thing resembles another but a metaphor boldly declares that one this is another. Hand your friend a photograph of your husband and tell her "This is my husband." Your friend will not conclude that you are married to a piece of paper with an image on it. She will understand that the image is a likeness of your husband. In Greek, it is clear that metaphor is being used. Greek requires that pronouns match the number and gender of the noun it refers to. In the phrase "this is my body," "this" and "my body" are in the neuter form, but "this" is clearly referring to the bread Jesus took. "Bread" is in the masculine form. This would be a violation of Greek grammar -- except when it is done to flag a metaphor.
What is being meant? Jesus is establishing a memorial by which his followers will remember his death until his return. "For I received from the Lord that which I also delivered to you, that the Lord Jesus in the night in which He was betrayed took bread; and when He had given thanks, He broke it and said, 'This is My body, which is for you; do this in remembrance of Me.' In the same way He took the cup also after supper, saying, 'This cup is the new covenant in My blood; do this, as often as you drink it, in remembrance of Me.' For as often as you eat this bread and drink the cup, you proclaim the Lord's death until He comes" (I Corinthians 11:23-26). The bread helps us remember Jesus' broken body upon the cross and the fruit of the vine helps us remember Jesus' shed blood. In partaking we are declaring to the world that we will not forget what Jesus did on our behalf.
But if your relative doesn't want to understand, she will deny the obvious and you won't be able to change her mind.