Here's an excerpt from a post I made on Mi Yoedya. I figured it applied here as well.
In 1 Corinthians 13:12, the apostle Paul wrote,
βλέπομεν γὰρ ἄρτι δι᾽ ἐσόπτρου ἐν αἰνίγματι τότε δὲ πρόσωπον πρὸς πρόσωπον ἄρτι γινώσκω ἐκ μέρους τότε δὲ ἐπιγνώσομαι καθὼς καὶ ἐπεγνώσθην
I would like for you to notice a couple of words: ἐσόπτρου, αἰνίγματι, πρόσωπον πρὸς πρόσωπον.
ἐσόπτρου (esoptrou) is the genitive inflection of ἔσοπτρον (esoptron). The Vulgate translates it into Latin as speculum. ἔσοπτρον is sometimes translated as "mirror" or "glass" (see A.V. in 1 Cor. 13:12; Jam. 1:23), but the ancients didn't have glass mirrors as we have today.
Rather, they used a polished piece of metal in order to see themselves (e.g., Pliny, Natural Histories, Book 33, §45). In time, a polished piece of metal will dull and oxidize, causing the appearance of the object in the mirror to become obscured. Thus, while the person looking into the mirror is looking at himself, the obscurity precludes him from actually seeing a reality.
Therefore, Paul writes that "we now see by a 'mirror' ἐν αἰνίγματι." The A.V. translates ἐν αἰνίγματι (en ainigmati) as "darkly." We find an inflection of the same word in Num. 12:8, which Paul is likely alluding to intentionally.
Regarding Moshe, G-d states,
I will speak with him mouth-to-mouth, even apparently, and not in dark speeches (LXX: αἰνιγμάτων), and he will behold the similitude of G-d...
The idea is that Moshe understood G-d directly, since G-d spoke to him "mouth-to-mouth." On the other hand, others understood G-d incompletely due to "dark speeches" (αἰνιγμάτων), or "obscurities."
In the Babylonian Talmud, we find an expression similar to Paul's. The rabbis were attempting to resolve the supposed contradiction between Isa. 6:2 ("I saw G-d") and Exo. 33:20 ("no man can see Me and live").
In tractate Yevamot 49b, it is written,
"I saw G-d" is [understood] in accordance with what was taught: All the prophets looked into a 'mirror' (אספקלריא) that is not clear, but Moshe looked into a clear 'mirror' (אספקלריא).
ואראה את ה' כדתניא כל הנביאים נסתכלו ב שאינה מאירה משה רבינו נסתכל באספקלריא המאירה
The word אספקלריא is a loan word derived from the Latin word "speculum," the same word found in the Vulgate for the Greek word ἔσοπτρον, the same Greek word found in 1 Cor. 13:12.
Again, this is an excerpt, but I thought it could be of some benefit.