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You posted before I finished editing my post, so the rest of my answer is in it.

Sometimes, when speaking of an impossible situation, we say: "Even if that could happen, then..." etc. This is the context in which he was speaking. It becomes quite clear when reading the whole passage.

4. And first of all, inasmuch as the divine poet throughout his whole life professed in exemplary manner the Catholic religion, he would surely desire that this solemn commemoration should take place, as indeed will be the case, under the auspices of religion, and if it is carried out in San Francesco in Ravenna it should begin in San Giovanni in Florence to which his thoughts turned during the last years of his life with the desire of being crowned poet at the very font where he had received Baptism. Dante lived in an age which inherited the most glorious fruits of philosophical and theological teaching and thought, and handed them on to the succeeding ages with the imprint of the strict scholastic method. Amid the various currents of thought diffused then too among learned men Dante ranged himself as disciple of that Prince of the school so distinguished for angelic temper of intellect, Saint Thomas Aquinas. From him he gained nearly all his philosophical and theological knowledge, and while he did not neglect any branch of human learning, at the same time he drank deeply at the founts of Sacred Scripture and the Fathers. Thus he learned almost all that could be known in his time, and nourished specially by Christian knowledge, it was on that field of religion he drew when he set himself to treat in verse of things so vast and deep. So that while we admire the greatness and keenness of his genius, we have to recognize, too, the measure in which he drew inspiration from the Divine Faith by means of which he could beautify his immortal poems with all the lights of revealed truths as well as with the splendours of art. Indeed, his Commedia, which deservedly earned the title of Divina, while it uses various symbolic images and records the lives of mortals on earth, has for its true aim the glorification of the justice and providence of God who rules the world through time and all eternity and punishes and rewards the actions of individuals and human society. It is thus that, according to the Divine Revelation, in this poem shines out the majesty of God One and Three, the Redemption of the human race operated by the Word of God made Man, the supreme loving-kindness and charity of Mary, Virgin and Mother, Queen of Heaven, and lastly the glory on high of Angels, Saints and men; then the terrible contrast to this, the pains of the impious in Hell; then the middle world, so to speak, between Heaven and Hell, Purgatory, the Ladder of souls destined after expiation to supreme beatitude. It is indeed marvellous how he was able to weave into all three poems these three dogmas with truly wrought design. If the progress of science showed later that that conception of the world rested on no sure foundation, that the spheres imagined by our ancestors did not exist, that nature, the number and course of the planets and stars, are not indeed as they were then thought to be, still the fundamental principle remained that the universe, whatever be the order that sustains it in its parts, is the work of the creating and preserving sign of Omnipotent God, who moves and governs all, and whose glory risplende in una parte piu e meno altrove; and though this earth on which we live may not be the centre of the universe as at one time was thought, it was the scene of the original happiness of our first ancestors, witness of their unhappy fall, as too of the Redemption of mankind through the Passion and Death of Jesus Christ. Therefore the divine poet depicted the triple life of souls as he imagined it in a such way as to illuminate with the light of the true doctrine of the faith the condemnation of the impious, the purgation of the good spirits and the eternal happiness of the blessed before the final judgment.