1 Corinthians 14:21: Gift of Tongues Prophesied in The Law

 In The Law [nomo] [1] it is written "With other tongues and strange lips will I speak to this people." 

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[1] There is controversy concerning many of Paul's references to "the Law," as to whether he was referring to the first five books of Moses only or to extra-scriptural rabbinical writings. In 1 Corinthians 14:21, we see an Old Covenant prophecy of the New Covenant gift of tongues along with an instance of Paul referring to the writings of the prophets as The Law.

The context of this verse determines that in his usage of the Greek word, nomo [in a quote of Isaiah 28:11], he was not referring to extra-scriptural rabbinical writings. 

Even though scripture does [in places] differentiate between the sacred writings of the Old Covenant, as “The Law and The Prophets,” the apostle did sometimes refer to the entirely of the Old Testament, “The Law and The Prophets,” as nomo. 

This is an excerpt from The Hungry Hearts Bible Commentary