26 Touching which matter, there will be some place open for consideration, if first the divine authorities which forbid a lie be diligently discussed: for if these give no place, we vainly seek a loophole; for we are bound to keep in every way the command of God, and the will of God in all that through keeping His command we may suffer, it is our duty with an even mind to follow: but if by some relaxation any outlet be allowed, in such a case we are not to decline a lie.
The reason why the Divine Scriptures contain not only God's commands, but the life and character of the just, is this: that, if haply it be hidden in what way we are to take that which is enjoined, by the actions of the just it may be understood. With the exception, therefore, of those actions which one may refer to an allegorical significance, although none doubts that they really took place, as is the case with almost all the occurrences in the books of the Old Testament. For who can venture to affirm of any thing there, that it does not pertain to a figurative foretelling?
Seeing the Apostle, speaking of the sons of Abraham, of whom of course it is most easily said that they were born and did live in the natural order of propagating the people, (for not monsters and prodigies were born, to lead the mind to some presignification,) nevertheless asserts that they signify the two Testaments; and says of that marvellous benefit which God bestowed upon His people Israel to rescue them out of the bondage in which they in Egypt were oppressed, and of the punishment which avenged their sin on their journey, that these things befell them in a figure: what actions will you find, from which you may set aside that rule, and take upon you to affirm that they are not to be reduced to some figure?
Excepting therefore these, the things which in the New Testament are done by the Saints, where there is a most evident commending of manners to our imitation, may avail as examples for the understanding of the Scriptures, which things are digested in the commands.
Source: On Lying (New Advent)