The disciples gradually saw the resurrection for what it really was, the start of the prophesied new creation.  Something earth-shaking had happened that changed their worldview.  They were the witnesses and “could not but speak the things they had seen and heard”. They now know that through Jesus of Nazareth, new creation has already begun.  It is seen in the first-of-a-kind body of Jesus.  Their body would ultimately be like His.  They were astonished and worshiped.

“So if anyone is in Christ, there is a new creation: everything old has passed away; see, everything has become new!” 2 Corinthians 5:17 (NRSV)