This admonition I have often given elsewhere I repeat here and shall give again: that the Christian reader should make it his first task to seek out the literal sense, as they call it. For it alone is the whole substance of faith and Christian theology; it alone holds its ground in trouble and trial, conquers the gates of hell (Matt. 16:18) together with sin and death, and triumphs for the praise and glory of God. Allegory, however, is too often uncertain, and is unreliable and by no means safe for supporting faith. Too frequently it depends on human guesswork and opinion, and if one leans on it, one will lean on a staff of Egyptian reed (Ezek. 29:6). Therefore we should beware of Jerome, Origen, and similar fathers or read them with independent judgment. Yes, we should beware of that whole Alexandrian school, which the Jew Philo extols, according to the testimony of Eusebius and Jerome, for having once excelled in the pursuit of such allegorical interpretation. For later writers unhappily imitated their example; which was adopted with excessive praise. They constructed and taught arbitrarily from Scripture according to their liking, until some shaped the words of God into the most absurd monstrosities; and, as Jerome also complains about his own time, they drag Scripture into contradiction with itself by citing proofs that do not apply, a crime of which he himself was also guilty.
Such are those who nowadays expound almost the whole Bible, wherever they find a word in the feminine gender, concerning the Blessed Virgin. Likewise those who build monasteries from the dwelling place of Martha and make our schoolmasters out of the mighty in Israel, and numberless similar wonders. One was even found who applied the whole of the Metamorphoses of Ovid to Christ, at which Jerome is properly indignant; in the Epistle to Paulinus he calls them peddlers. Hence the rule of Paul should be observed here, that allegories should be kept in second place and be applied for the strengthening, adorning, and enriching of the doctrine of faith, or, as he says in 1 Cor. 3:11 ff., they should not be the foundation but be built on the foundation, not as hay, wood, and stubble but as silver, gold, and gems. This is done when, according to the injunction of Rom. 12:6, prophecy is according to the analogy of faith, namely, that you first take up a definite statement set down somewhere in the Scriptures, explain it according to the literal sense, and then at the end connect to this an allegorical meaning which says the same thing. Not as though the allegorical meaning proved or supported the statement of doctrine; but it is proved or supported by the statement, just as a house does not hold up the foundation but is held up by the foundation.
Luther’s works, vol. 9: Lectures on Deuteronomy 1525