2 Then, after His reproach, what says He? “There shall no sign be given to it, but the sign of Jonas the prophet.” Now is He striking the first note of the doctrine of His resurrection, and confirming it by the type.
What then? One may say; was no sign given it? None was given to it on asking. For not to bring in them did He work His signs (for He knew them to be hardened), but in order to amend others. Either then this may be said, or that they were not to receive such a sign as that was. For a sign did befall them, when by their own punishment they learned His power. Here then He speaks as threatening, and with this very meaning obscurely conveyed: as if He said, innumerable benefits have I showed forth, none of these has drawn you to me, neither were ye willing to adore my power. You shall know therefore my might by the contrary tokens, when you shall see your city cast down to the ground, the walls also dismantled, the temple become a ruin; when you shall be cast out both from your former citizenship and freedom, and shall again go about everywhere, houseless and in exile. (For all these things came to pass after the cross.) These things therefore shall be to you for great signs. And indeed it is an exceeding great sign, that their ills remain unchanged; that although ten thousand have attempted it, no one has been able to reverse the judgment once gone forth against them.
All this however He says not, but leaves it to after time to make it clear to them, but for the present He is making trial of the doctrine of His resurrection, which they were to come to know by the things which they should afterwards suffer.
“For as Jonas,” says He, “was three days and three nights in the whale's belly, so shall the Son of Man be three days and three nights in the heart of the earth.” Thus, He said not indeed openly that He should rise again, since they would have even laughed Him to scorn, but He intimated it in such manner, that they might believe Him to have foreknown it. For as to their being aware of it, they say to Pilate, “That deceiver said,” these are their words, “while He was yet alive, After three days I will rise again;” and yet we know His disciples were ignorant of this; even as they had been beforehand more void of understanding than these: wherefore also these became self-condemned.
But see how exactly He expresses it, even though in a dark saying. For He said not, “In the earth,” but, “In the heart of the earth;” that He might designate His very sepulchre, and that no one might suspect a mere semblance. And for this intent too did He allow three days, that the fact of His death might be believed. For not by the cross only does He make it certain, and by the sight of all men, but also by the time of those days. For to the resurrection indeed all succeeding time was to bear witness; but the cross, unless it had at the time many signs bearing witness to it, would have been disbelieved; and with this disbelief would have gone utter disbelief of the resurrection also. Therefore He calls it also a sign. But had He not been crucified, the sign would not have been given. For this cause too He brings forward the type, that the truth may be believed. For tell me, was Jonah in the whale's belly a mere appearance? Nay, you can not say so. Therefore neither was Christ in the heart of the earth such. For surely the type is not in truth, and the truth in mere appearance. For this cause we every where show forth His death, both in the mysteries, and in baptism, and in all the rest. Therefore Paul also cries with a clear voice, “God forbid that I should glory, save in the cross of our Lord Jesus Christ.”
Whence it is clear, that they who are diseased in Marcion's way are children of the devil, blotting out these truths, to avoid the annulling whereof Christ did so many things, while to have them annulled the devil took such manifold pains: I mean, His cross and His passion.
Source: Homilies on the Gospel of St. Matthew (New Advent)