As St. John Chrysostom so eloquently notes, NOTHING worldly can account for the transformation in the Apostles from the cowardly, confused, bumbling men before Christ's death, to the warriors they became after Pentecost.
"How then account for the fact that these men, who in Christ's lifetime did not stand up to the attacks by the Jews, set forth to do battle with the whole world once Christ was dead - if, as you claim, Christ did not rise and speak to them and rouse their courage? Did they perhaps say to themselves: "He could not save himself but he will protect us? He did not help himself when he was alive, but now that he is dead he will extend a helping hand to us? In his lifetime he brought no nation under his banner, but by uttering his name we will win over the whole world?" Would it not be wholly irrational even to think such thoughts, much less to act upon them? It is evident, then that if they had not seen him risen and had proof of his power, they would not have risked so much."