I have also heard conjecture that the reason we do not know is because the original introduction has been lost. If you think about it, "God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets..." is a rather abrupt beginning to a letter. Usually, you say, "Dear friends", or at least, "To Whom It May Concern." But the way that it appears in our Bibles seems a little curt and impolite.

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