The point of having a physical body that enjoys the world is to teach our souls to enjoy HaShem in the same way. This is the teaching of the Holy Pri Ha'aretz on Parashath Ki Tisa.
If we don't teach our neshama how to enjoy in HaShem, then when the body expires, the soul is left with no source of sustenance, and it expires as well (heaven forbid) this is what being cut off (כרת) is.