Already above [I have] indicated certain [things] from Josephus; but the text recounts three. The first: “And Moses built an altar.” Namely, that he might show his own most grateful spirit, and [that] of all the Israelites — [gratitude] toward that divine power, from whom [came] so great a triumph — [and that] he might publicly give thanks to him with a festal victim; and by that very [act] might admonish all — both the Israelites [then] present, and also us — what [is] to be done after the good fortune of wars. In the first of those rules of warfare which Ferrandus of Carthage prescribes to the illustrious Leader in Africa: “Ascribe nothing proudly to thy own strength; but all [things] which thou doest wisely, or bravely, or successfully, bear [refer] to the praise of the most powerful Creator.” But because the Innovators of this most recent time — from the so frequent mention of Christian altars which is among the Fathers — shrink from acknowledging a Christian sacrifice, let them acknowledge their own [Calvin] here speaking thus: “Moses built an altar; namely, that by a solemn sacrifice he might make his gratitude attested — not he only, but the whole people. Which very [thing] the name of altar shows.” See Bellarmine (book 1 On the Mass, ch. 16). But this too is to be observed: [that] it was not by [any] precept to Moses that he did this — and yet…
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…and yet he did [it] most rightly — so that those same Innovators may learn not to spurn those [things] which are called works of supererogation, [namely] goods indeed, and unbidden. The law of nature alone, indeed, prescribed [that] he render thanks to God; but that [he do it] in this way — by an altar, by a sacrifice — neither that [law], nor any divine [law] promulgated at that very time, defined. But someone will perhaps ask why, whereas Moses had before prescribed certain [things] to Joshua, it is written (v. 10), “Joshua did as Moses had spoken”; but when God commanded to Moses himself those [things] which were said [in] questions 19 and 20, it is not similarly said, “Moses did as the Lord had spoken”? I think [it is] because it was clear enough that he had done [it]. For who would doubt [that he] who did so studiously even the [things] which were not commanded, most promptly and most carefully performed at once the [things] which were commanded by God?