In this excerpt, Origen considers the clouds to be symbols of the prophets and apostles, whose divine words fell upon the Earth like rain.
"φωνὴν ἔδωκαν αἱ νεφέλαι."
πάλιν ἐὰν τροπολογίαν θέλωμεν,
πολλάκις εἰρήκαμεν. καὶ
μάλιστα διὰ τὸ "ταῖς νεφέλαις ἐντελοῦμαι
τοῦ μὴ βρέξαι ὑετὸν ἐπ᾽αὐτον." (Is. 5:6)
τίνα δὲ, ἢ "τὸν ἀμπελῶνα
τὸν οἶκον τοῦ Ισραήλ." καὶ ἡ ἀλήθεια
δὲ τοῦ θεοῦ, φθάνει ἕως
τῶν νεφελῶν, ἀλλ᾽εἰσὶ τινὲς δίκαιοι
ἐπαιρόμενοι ἀπὸ τῆς γῆς
σώμασι, καὶ γενόμενοι νεφέλαι.
τοιοῦτος ἦν Μωϋσῆς λέγων, "πρόσεχε
ὁ οὐρανὲ καὶ λαλήσω, καὶ ἀκουέτω
γῆ ῥήματα ἐκ στόματός μου.
προσδοκάσθω ὡς ὑετὸς τὸ ἀπόφθεγμά μου."
εἶτα ὥσπερ ὑετοῦ σωματικοῦ
καὶ ἀψύχου, ἡ νεφέλη αὐτὴ
ἔλεγεν ἄν, "προσδοκάσθω ὡς ὑετὸς
καὶ ὁ ἐμὸς λόγος," οὕτως ἐπεὶ Μωϋσῆς
λέγεται νεφέλη ἦν, ἔλεγε, "προσδοκάσθω
ὡς ὑετὸς τὸ ἀπόφθεγμά μου,
καὶ καταβήτω ὥς δρόσος τὰ
ῥήματά μου," καὶ ἐπεὶ νεφέλη ἦν, ἔλεγεν
"ὡσεὶ ὄμβρος ἐπ᾽ἄγρωστιν,
καὶ ὡσεὶ νιφετὸς ἐπὶ χόρτον,
ὅτι ὄνομα κυρίου ἐκάλεσα." (Dt. 32:2-3)
τοιοῦτοι ἦσαν πάντες, οἱ ἐκλεκτοὶ προφῆται,
οἱ θαυμάσιοι ἀπόστολοι.
"The clouds gave a voice." Again, if we choose allegory, will shall have much to say, and especially because of the scripture, "I will command the clouds to not rain upon it." (Is. 5:6) Upon what? Upon "the vineyard that is the house of Israel." Also there is the scripture, "the truth of God reaches unto the clouds," but there are also some righteous men who have been lifted from the earth while in their bodies, and have become clouds. Such was Moses, saying, "harken O heaven, and I will speak. Let the earth listen to the words from my mouth. Let my message be yearned for like rain."
So then, if this was a cloud of normal, physical rain, he would have said, "May my word be yearned for, even as rain." But since Moses is said to be a cloud, he said, “Let my message be yearned for as rain, and let my words fall as dew.” Likewise, since he was a cloud, he continued, “and as a rainstorm upon the greenery, and as a snowstorm upon the grass, for I have called upon the name of the Lord.” All of the chosen prophets and the wondrous apostles were as such.