I. The events recorded as happening after the Resurrection were intended to convince us of its truth
Since the blessed and glorious Resurrection of our Lord Jesus Christ, whereby the Divine power in three days raised the true Temple of God, which the wickedness of the Jews had overthrown, the sacred forty days, dearly-beloved, are today ended, which by most holy appointment were devoted to our most profitable instruction, so that, during the period that the Lord thus protracted the lingering of His bodily presence, our faith in the Resurrection might be fortified by needful proofs.
For Christ's Death had much disturbed the disciples' hearts, and a kind of torpor of distrust had crept over their grief-laden minds at His torture on the cross, at His giving up the ghost, at His lifeless body's burial. For, when the holy women, as the Gospel-story has revealed, brought word of the stone rolled away from the tomb, the sepulchre emptied of the body, and the angels bearing witness to the living Lord, their words seemed like ravings to the Apostles and other disciples.
Which doubtfulness, the result of human weakness, the Spirit of Truth would most assuredly not have permitted to exist in His own preacher's breasts, had not their trembling anxiety and careful hesitation laid the foundations of our faith. It was our perplexities and our dangers that were provided for in the Apostles: it was ourselves who in these men were taught how to meet the cavillings of the ungodly and the arguments of earthly wisdom. We are instructed by their lookings, we are taught by their hearings, we are convinced by their handlings. Let us give thanks to the Divine management and the holy Father.' necessary slowness of belief. Others doubted, that we might not doubt.
Source: Sermons (New Advent)