What does venerable Sariputta mean by "dwelling withdrawn"?

In Bhikkhu Bodhi's "In the Buddha's Words", venerable Sariputta gives a discourse on "The Conditions for Wisdom", which contains eight causes and conditions for obtaining wisdom. He says, > Having learned the Dhamma, he dwells withdrawn by way of two kinds of withdrawal: withdrawal of body and withdrawal of mind. This is the third cause and condition for obtaining the wisdom fundamental to the spiritual life.... (AN 8:2, abridged; IV 151-155) pg. 322 What does it mean to be withdrawn in these two ways? Thank you