'Maghavat, this body is mortal and always held by death. It is the abode of that Self which is immortal and without body. When in the body (by thinking this body is I and I am this body) the Self is held by pleasure and pain. So long as he is in the body, he cannot get free from pleasure and pain. But when he is free of the body (when he knows himself different from the body), then neither pleasure nor pain touches him.

In plain words: Prajapati teaches that the body is mortal and always in death's grip, but it is the home of the Self, which is deathless and has no body. As long as you think "I am this body," you are caught by pleasure and pain; when you know you are different from the body, pleasure and pain no longer touch you.