Derek,

>> But what is the point of such a statement? What is it telling us that we

don't already know?<<

Try reading it in the greater context:
"In this way he remains focused internally on the body in & of itself, or
externally on the body in & of itself, or both internally & externally on
the body in & of itself. Or he remains focused on the phenomenon of
origination with regard to the body, on the phenomenon of passing away with
regard to the body, or on the phenomenon of origination & passing away with
regard to the body. Or his mindfulness that 'There is a body' is maintained
to the extent of knowledge & remembrance. And he remains independent,
unsustained by (not clinging to) anything in the world. This is how a monk
remains focused on the body in & of itself."

This is during breath meditation. The sense of a body can slip away, but
this is simply keeping it in mind. In some way one is mindful of the body
even if it is just the mindfulness, 'there is a body.'

Sean