[It] cannot come to pass that servants cannot serve [their] Creator, and men [their] Lord. For that [man] would be a Tyrant, who should command these [servants that] which [they] could not do; [and] Joshua would be insane, who should give an option of things which cannot be done — nay, [who should] admonish and exhort to those [impossible things]. All Interpreters, therefore, deny [that] that [saying] which Joshua says — “You will not be able to serve” — is to be taken absolutely, but [only] in a modified [modificate] and restricted [way]. But the modification and restriction is handed down by many [as] manifold. First: by S. Augustine (here, q. 28): “You will not be able [to serve], by your [own] strength, without God’s help and mercy.” Second: by the same [one] in the same place: “You will not be able [to serve] perfectly, and without any offense.” Third: by Abulensis (q. 12): “You will not be able [to serve] with impunity, without divine wrath and penalty.” Fourth: by the same [one] in the same place: “You will not be able [to serve] easily; but only with [great] difficulty” — in that mode, namely, by which Aristotle (Physics bk. 3, ch. 3, text 34) says [that] something infinite [can] “with difficulty, or scarcely, be finished” and crossed through. Fifth: by Caietanus [Cajetan]: “You will not be able [to serve] constantly and for long.” Sixth: by others: “You will not be able [to serve] together with the worship of idols.”
[It] seems to me [that] this negation — “You will not be able to serve the Lord” — is a most vehement exhortation to serving him. For [those] who see [that] some [persons] wish something, and desire [that] they wish it still more, are wont to say to them: “You will not be able to do, to have, [or] to obtain this.” For by this mode of speaking, [it] is not simply denied [that] they are able [to do] that; but some mode and condition is understood, which he who so speaks understands, and which is either known or cared about by him to whom [it] is spoken. For example: let [there] be a Commander who wishes to sharpen and stir up more certain soldiers who are about to undertake some [enterprise]; [he] first sets before them their [own] fewness, the difficulty of the matter, [and] the magnitude of the dangers which are about to befall: and then [he] says: “You will not be able [to accomplish] that which you have undertaken — [namely] to conquer the enemy — unless you put on great courage, [and] are prepared to endure the greatest labors and perils, and hold [it] decreed and fixed in [your] mind either to fall or to conquer. But if indeed you are of so generous a spirit and so excellent a virtue, you will certainly accomplish that which you are revolving in [your] mind; and [that] you may be such, and may straightway undertake the business, I vehemently wish, exhort, and — by God, and by all [things] dear to you — beseech [you].” What [of] those soldiers here? Will [they] despond in spirit from that first negation of the Commander? Do [they] not understand [that it] is not an absolute and precise negation, but [one that] rather requires certain conditions? And will [they] not at once accept these? Will [they] not be the more incited, that [they] may undertake the virtue, endurance, and excellence of spirit to which the good Leader hinted [to] them? [that they] may rush bravely into all labors and dangers? and not acquiesce before [they] have rendered that matter accomplished? So indeed Joshua, when [he] had seen the Israelites choosing God before all [false] gods, and had been affected with great joy on account of that election, nevertheless wished to render them, in that matter, still more inflamed, more diligent, and more persevering. He knew their [disposition], especially prone to vices and to idolatry, [their] over-headlong nature. [He] knew the depraved custom of certain [people] — of complaining and murmuring in adversities, of running riot in favorable and prosperous [times], and of forgetting divine [things]. [He] knew [that] many occasions, enticements, and frauds — [tending] toward all-kinds-of sins and toward the desertion of God — would befall them from the remaining Canaanites, from the surrounding idolatrous nations, and from the devil and the flesh. For all these [things], how most fortified and most attentive Joshua wishes [them] to be — so that [they] may strive to overcome these [things] thereafter; [so] that [they] may most studiously and most strongly turn aside all occasions of sins, incitements to idolatry, [and] the stocks and seeds of wickedness; [so] that [they] may suffer themselves to be led away by no matter from God and from his most holy worship, but in it — with divine grace and help — may persist and persevere most eagerly, most constantly, and most perfectly, as far as is lawful for mortals. And [so] that [he] may excite in them this desire, ardor, and impetus; [so] that [he] may instigate [them, having been] admonished [of] the depravity of [their] secretly and covertly concealed viciousness, to the keeping of themselves thereafter and to a serious care [of themselves]; [so] that [they] may be made most prompt, and most willing and voluntary, toward the worship of that same God — all difficulties also considered — now [he] says: “You will not be able to serve the Lord” — namely, as [it] behooves: purely, chastely, wholly, long, and constantly — unless [you] henceforth beware, and with [your] mind cultivate his laws and ceremonies with the greatest [care].
And this can also be understood from the reasons [arguments], four [in number], which [Joshua] joins to this his saying. First: “For God [is] holy.” [He] wishes, therefore, to be worshiped in a holy manner, [and] purely and chastely. And in Hebrew [it] is in the plural: “elohim cedoschim” [אלהים קדשים], that is, “God very holy,” “most holy,” or precisely — and without any addition — “holy,” as [it] is in our Interpreter [Vulgate], and [in] the Seventy: ὅτι ὁ Θεὸς ἅγιός ἐστι [hoti ho Theos hagios esti, “because God is holy”]; as [in] Jeremiah 10:10: “the living God,” in Hebrew “the living [ones]” [plural]. Second: “And [he] is a strong emulator [jealous]” — or “zealot” [zelotes], as in the Seventy: ζηλώσας [zēlōsas, “being jealous, zealous”]. Nothing, therefore, [is] to be admitted against him which is at all more grave, and which overturns his sacred [rites] and religion. Third: From the effect of this divine zeal. “Nor will [he] forgive your wickednesses and sins” — which, as I said, overturn his worship, [and] are great scandals, [and] offend him more gravely, as follows (v. 20). Fourth: “If you leave the Lord, and serve strange Gods, [he] will turn, and will afflict you, and will overthrow [you] after [he] has bestowed good [things].” Lest, therefore, any of these evils befall you — which [God] forbid! — and because [you] have such a God, serve [him], serve him, O Israelites, with [your] whole heart, and [your] whole soul, most religiously, most accurately, [and] most perseveringly. In this way the people understood [it]: and therefore [it] responded [that] [it] would so do, and promised [it] (vv. 21, 22, 24).