1 Faustus said: If you ask why we do not believe Moses, it is on account of our love and reverence for Christ. The most reckless man cannot regard with pleasure a person who has cursed his father. So we abhor Moses, not so much for his blasphemy of everything human and divine, as for the awful curse he has pronounced upon Christ the Son of God, who for our salvation hung on the tree. Whether Moses did this intentionally or not is your concern. Either way, he cannot be excused, or considered worthy of belief.
His words are, "Cursed is every one that hangs on a tree." You tell me to believe this man, though, if he was inspired, he must have cursed Christ knowingly and intentionally; and if he did it in ignorance, he cannot have been divine. Take either alternative. Moses was no prophet, and while cursing in his usual manner, he fell ignorantly into the sin of blasphemy against God. Or he was indeed divine, and foresaw the future; and from ill-will to our salvation, he directs the venom of his malediction against Him who was to accomplish that salvation on a tree.
He who thus injures the Son cannot surely have seen or known the Father. He who knew nothing of the final ascension of the Son, cannot surely have foretold His advent. Moreover, the extent of the injury inflicted by this curse is to be considered. For it denounces all the righteous men and martyrs, and sufferers of every kind, who have died in this way, as Peter and Andrew, and the rest. Such a cruel denunciation could never have come from Moses if he had been a prophet, unless he was a bitter enemy of these sufferers.
For he pronounces them cursed not only of men but of God. What hope, then, of blessing remains to Christ, or his apostles, or to us if we happen to be crucified for Christ's sake? It indicates great thoughtlessness in Moses, and the want of all divine inspiration, that he overlooked the fact that men are hung on a tree for very different reasons, some for their crimes, and others who suffer in the cause of God and of righteousness. In this thoughtless way lie heaps all together without distinction under the same curse; whereas if he had had any sense, not to say inspiration, if he wished to single out the punishment of the cross from all others as specially detestable, he would have said, Cursed is every guilty and impious person that hangs on a tree.
This would have made a distinction between the guilty and the innocent. And yet even this would have been incorrect, for Christ took the malefactor from the cross along with himself into the Paradise of his Father. What becomes of the curse on every one that hangs on a tree? Was Barabbas, the notorious robber, who certainly was not hung on a tree, but was set free from prison at the request of the Jews, more blessed than the thief who accompanied Christ from the cross to heaven?
Again, there is a curse on the man that worships the sun or the moon. Now if under a heathen monarch I am forced to worship the sun, and if from fear of this curse I refuse, shall I incur this other curse by suffering the punishment of crucifixion? Perhaps Moses was in the habit of cursing everything good. We think no more of his denunciation than of an old wife's scolding. So we find him pronouncing a curse on all youths of both sexes, when he says: "Cursed is every one that raises not up a seed in Israel." This is aimed directly at Jesus, who, according to you, was born among the Jews, and raised up no seed to continue his family.
It points too at his disciples, some of whom he took from the wives they had married, and some who were unmarried he forbade to take wives. We have good reason, you see, for expressing our abhorrence of the daring style in which Moses hurls his maledictions against Christ, against light, against chastity, against everything divine. You cannot make much of the distinction between hanging on a tree and being crucified, as you often try to do by way of apology; for Paul repudiates such a distinction when he says, "Christ has redeemed us from the curse of the law, being made a curse for us; as it is written, Cursed is every one that hangs on a tree."
Source: Reply to Faustus the Manichaean (New Advent)