John chapter 20 records a series of resurrection revelations. John & Peter realized Jesus was risen only upon touring the empty tomb and witnessing the carefully folded grave clothes of our Lord (3-8). Next, Mary Magdalene remains distraught despite witnessing the empty tomb and angels until Jesus Himself speaks to her from the garden (11-18). Jesus then visits a meeting of disciples cowering behind locked doors for fear of the Jews. He shows them his crucifixion wounds and speaks a blessing of peace restoring their joy (19-23). Finally, eight days later, the doubts of Thomas are assuaged only when Christ appears to him in the flesh and the disciple touches his pierced hands and side (224-28).
Verse 9 of this chapter explains why these face to face encounters were necessary…”for as yet they did not understand the Scripture, that he must rise from the dead.” This would not always be the case however, shortly after these events and the Pentecost advent of the Holy Spirit, Peter began to proclaim the Gospel from the OT scriptures. It is this witness combined with the NT accounts that now serves to open our eyes and hearts to believe. Behold Peter preaching after he understood the scripture proclaiming Christ.