But the ambiguities of metaphorical words, about which I am next to speak, demand no ordinary care and diligence. In the first place, we must beware of taking a figurative expression literally. For the saying of the apostle applies in this case too: “The letter killeth, but the spirit giveth life.”
 
[Sed verborum translatorum ambiguitates, de quibus deinceps loquendum est, non mediocrem curam industriamque desiderant. Nam in principio cavendum est ne figuratam locutionem ad litteram accipias. Et ad hoc enim pertinet quod ait Apostolus: Littera occidit, spiritus autem vivificat.]

Augustine of Hippo (354-430) Christian church father, philosopher, saint [b. Aurelius Augustinus]

On Christian Doctrine [De Doctrina Christiana], Book 3, ch. 5 / § 9 (3.5.9) (AD 397) [tr. Shaw (1858)]
    (Source)

Quoting 2 Cor. 3:6.

(Source (Latin)). Alternate translations:

But the ambiguities of figurative words, which are now to be treated, require no little care and industry. For at the outset you must be very careful lest you take figurative expressions literally. What the apostle says pertains to this problem: "For the letter killeth, but the spirit quickeneht."
[tr. Robertson (1958)]

But the ambiguities of metaphorical words, about which I must now speak, require no ordinary care and attention. To begin with, one must take care not to interpret a figurative expression literally. What the apostle says is relevant here: "the letter kills but the spirit gives life."
[tr. Green (1995)]