# for it must be treated by you as holy

"for you must treat it as holy" 

# Everyone who defiles it

"Everyone who treats the Sabbath with disrespect" or "Everyone who does not obey the laws about the Sabbath" 

# must surely be put to death

"you must surely kill" or "you must surely execute"

# must surely be cut off from his people

Possible meanings: 1) "Yahweh will no longer consider him to be one of his people" 2) "you must surely send him away" or 3) "you must surely kill him."