Why may I not take Communion in a Lutheran Church?

Before returning to the Catholic Church, I attended the Lutheran Church with my step-mother. She is elderly, so I attend Mass on Saturday evenings in order to drive her to church on Sundays.
Upon returning to the Catholic Church, I made my reconciliation and was told by my priest I may continue to accompany my step-mother to church, but I may no longer take Communion there. For some reason, I failed to ask the question, “Why?”. I believe I KNOW the reason, but would you please enlighten me?

Thank you:confused:

These links should be helpful for understanding why there is no intercommunion with non-Catholics. If you have any further questions or concerns that are not answered by these links, please contact Catholic Answers directly.
Recommended Reading:
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[LIST]
*]Who Can Receive Communion?
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Ecclesia de Eucharistia **(Note especially sections 43-46)
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