The Bible does not explicitly mandate wheat flour for the Communion host. The Catholic Church, the Church Jesus established to teach in his name (cf. Matt. 16:18-19, 28:19-20; Luke 10:16), does mandate wheat flour for the Eucharist in its Code of Canon Law:
§1 The most holy sacrifice of the Eucharist must be celebrated in bread, and in wine to which a small quantity of water is to be added.
Although the Bible does not explicitly state that only wheat flour may be used for the eucharistic hosts, it does support the Church’s mandate in many places. For more information, please see the article linked below.
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