The physical resurrection of Jesus is all important to Christianity. If it did not occur then Christianity is shite.
A physical resurrection means Jesus is God and man. As Thomas the apostle said when viewing the hole in his hand. My Lord and My God.
We know Jesus rose from the dead on the third day because he was seen by a lot of witnesses. The Jewish religious leaders could not dispute this at all.
We also know because his apostles were changed men willing to die for him after this occurred. They did not hide as before and were not silent as before.
This is why Christianity spread.
On a side-issue Sinclair Davidson attempts to be too clever by half.
Sunday is the 1st day of the week not the 0th day. Saturday is the 7th day of the week not the 6th as Davidson attests!
Thursday is the 1st day of a cricket test in Australia not the 0th day. It last 5 days not 4 days!
Sometime when you try and be too clever you end up being very stupid.