Peter is a different man, different that when he was when he served as a disciple during your shoeless earthly ministry, what changed him, he witness the resurrection, he spoke to the resurrected Lord. And he also was a recipient of that Holy Spirit. Therefore being filled and in dwelt with the Holy Spirit, knowing the resurrected Savior, and remembering now with a different mindset, something that he had witness, all of these things caused him to be very different.