What does venerable Sariputta mean by "dwelling withdrawn"?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  Having learned the Dhamma, he dwells withdrawn by way of two kinds of withdrawal: withdrawal of body and withdrawal of mind.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What does it mean to be withdrawn in these two ways?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
Piya Tan's comment for AN 8.2:

The third factor that conduces to developing wisdom in an individual is aloneness of body and of mind (kāya,vūpakāsa citta,vūpakāsa), that is, cultivating aloneness of both the body and the mind. The word vūpakāsa (“estrangement, alienation, separation, seclusion”) comes from the verb vūpakāseti (causative of vavakassati, “to be drawn away, to withdraw”). It is found in only as a suffix (in fine compositi) to these two compounds: kāya,vūpakāsa and citta,vūpakāsa.10 These two terms also appear in the (Bojjhaṅga) Sīla Sutta (S 46.3), which should be studied with this Sutta.11
“Aloneness” is not “loneliness” (where we miss someone or something familiar). Here, aloneness is where we leave behind the world we were familiar with to face ourself so that we dedicate ourself fully to the spiritual life. It means being undistracted by the world and worldliness, and to commit all our body and heart to our training.

This quote is only the first subsection: see the PDF (pages 145 through 147) for further explanation (which describes bodily solitude, mental solitude, and spiritual solitude).