There was something powerful that happened to change the broken disciples of a dead religious leader and a lost cause into the confident proclaimers of good news. Something powerful changed the ignominy of execution on a cross into a symbol for life itself. Death was itself defeated by the Resurrection of Jesus the Christ. Something very powerful had changed everything.
Those who believed in the resurrection very early in the life of the faith were all Hebrews. Their Sabbath was sundown Friday to sundown Saturday but because of the resurrection their Sabbath was extended to include dawn on the first day of the week as well. The Hebrew followers of Jesus would fulfill their Jewish religious duties to God and then meet before they went to work to celebrate the resurrection of their Lord. At this dawn worship they would preach the Gospel, sing psalms, baptize new believers, and have communion.
Later when gentiles became Christians their worship would only be on the first day of the week. For the first three hundred years of the Christian faith the followers of Jesus would meet before and after work on the first day for worship. Then in 325 AD the Roman Empire got its first Christian emperor and the First day became an official day of worship and rest. So the resurrection of Jesus also changed the Sabbath for Christians from Saturday to Sunday. More importantly the resurrection of Jesus makes a difference in our relationship with God. Because of the resurrection we have salvation by the awesome grace of God. The resurrection difference is wonderful.