Ascension: "the disciples' slowness to believe that the Lord had indeed risen from the dead, was not so much their weakness as our strength"

From the Holy Gospel according to Mark
Mark 16:14-20
At that time, Jesus appeared unto the eleven disciples as they sat at meat, and upbraided them with their unbelief and hardness of heart, because they believed not them which had seen Him after He was risen. And so on.

Homily by Pope St. Gregory the Great
29th on the Gospels
I may be allowed to say that the disciples' slowness to believe that the Lord had indeed risen from the dead, was not so much their weakness as our strength. In consequence of their doubts, the fact of the Resurrection was demonstrated by many infallible proofs. These proofs we read and acknowledge. What then assureth our faith, if not their doubt? For my part, I put my trust in Thomas, who doubted long, much more than in Mary Magdalene, who believed at once. Through his doubting, he came actually to handle the holes of the Wounds, and thereby closed up any wound of doubt in our hearts.

Now confirm to our minds the trustworthiness of the fact that our Lord did indeed rise again from the dead, it is well for us to remark one of the statements of Luke Acts i. 4. "Eating together with them, He commanded them that they should not 1 John xiv. 16, 17 xvi. 7. depart from Jerusalem and a little afterward: "While they beheld, He was taken up, and a cloud received Him out of their sight." Consider these words, note well these mysteries. After "eating together with them He was taken up." He ate and ascended: that the fact of His eating might show the reality of the Body in Which He went up. But Mark telleth us that before the Lord ascended into heaven, He upbraided His disciples; with their unbelief and hardness of heart. From this I know not why we should gather, but that the Lord then upbraided His disciples, for whom He was about to be parted in the body, to the end that the words which He spoke unto them as He left them might be the deeper imprinted on their hearts.