Inwardness springs from unity. Ruusbroec is keeping the chain visible: only the soul whose powers have been gathered into one can turn into its own interior and find anything there. The dispersed soul cannot go inward because there is no inside to enter; what looks like inwardness for the dispersed person is just a different region of distraction. The Hesychast tradition reached the same diagnosis and made the gathering of the mind into the heart (synagein ton noun eis ten kardian) the precondition of all real prayer. The Sufi term is jamʿ, gathering. The dispersed self is not the self that prays.On Hesychast 'descent of the nous into the heart' see the Philokalia vol. IV (Theoleptos of Philadelphia); on Sufi jamʿ, al-Sarraj, Kitab al-Lumaʿ.
A sensible fire of love which the Spirit of God has blown to a flame, and which urges a man from within; and he knows not whence it comes nor what has befallen him. The phrase 'he knows not whence it comes' echoes John 3:8, the wind blowing where it lists. Ruusbroec is naming a particular phenomenology — the inward warming that arrives without an identifiable cause, that the soul recognizes as not its own work. The mature contemplative learns to recognize this kind of stirring and to cooperate with it; the immature one either explains it away or appropriates it as a personal achievement. The same description shows up in Rumi when he writes 'I did not know my heart's reason for these tears.'John 3:8; Rumi, Diwan-i Shams, the gazals on the inward weeping whose source the lover cannot name.