Now truly, when Moses and Joshua had left Aaron and the other elders in the lowest part of the mountain, they themselves ascended higher — yet not to the very peak of the mountain; and in that middle part, as it were, of the mountain they remained, as we heard, six days. “But on the seventh day,” says the text (Exodus ch. 24, v. 16), “the Lord called Moses from the midst of the darkness.” Behold, Moses alone is called out, not Joshua. And it is subjoined (v. 18): “And Moses, entering into the midst of the cloud, went up into the mount” — that is, into the highest part of the mountain. Behold again, Moses alone enters the midst of the cloud, Moses alone climbs to the loftiest peak, not Joshua. Yet when I consider with myself [that] earlier [it] was nowhere reported [that] it had been commanded [that] Joshua ascend together with Moses, and [that] we nevertheless saw he did ascend — nay, whereas [it] is expressly written (v. 2), “And Moses alone went up to the Lord,” and yet Joshua accompanied him — I am borne almost to the opinion that Joshua never departed from Moses’s side, but followed him wherever he went. For was not “Come up to me into the mount, and be there” (v. 12) able to seem said to Moses alone? — and yet it is subjoined (v. 13) [that] Joshua ascended together with him. The reason and causes of the ascent seem quite equal in both [cases], to each part of the mountain, which were brought above (q. 5) [to show] why in that ascent to the mid-height of the mountain he was rightly Moses’s companion — [and] all those same [reasons] join him assiduously to Moses [as he goes] to the higher [parts] too, [as] he approaches [them], and all but fasten him [there]. But to repeat these here [would be] unseasonable. And St. Ambrose truly seems to have had the same opinion settled in [his] mind, when (book 2 On Duties, ch. 20) he said: “Moses spoke with God; Jesus [Joshua] likewise was covered by the cloud.” Masius (on Joshua ch. 11, p. 211): “Joshua was next to Moses in that sacred colloquy, and all but admitted with him into the heavenly sanctuary on Mount Sinai.” But someone objecting [that] he could then have heard, when (Exodus 32) the Lord told Moses the people had sinned, and when [Moses interceded]…
(col. 123)
…[when Moses interceded] for it. I answer, 1. [that] this speech of God and Moses was interior, which Joshua could not hear. 2. [That] Joshua himself stood off from Moses by some interval still — as both will be said below, ch. 5, q. 1. You will press [that] Philo (in the book On Charity) denies [that Joshua] was with Moses at this time. “He was,” he says, “the companion and tent-mate of the Prophet — except when he [Moses] sought retirement, for the sake of the divine colloquies.” I answer [that] other retirements of Moses can be understood; or even, in this very retirement, [that] Moses sometimes withdrew still further from Joshua, that he might attend the divine [things] more privately — as [was] just now said: just as, in the garden, CHRIST the Lord [withdrew] from both kinds of disciples, both those whom he had left in the first part and those whom he had led with him into the latter and more inward [part].