God has to be searched and invoked in the secret of a rational soul, which is called the interior man.
(De magistro 1)
There is an origin and source of virtue. There is a root of wisdom. And, there is, so to speak, a region of changeless truth. If the soul leaves this region, it lives in darkness but, when it approaches this region, it is enlightened.
(En. in ps. 58, S 1, 18)
Whoever seeks joy in himself will be sad, but whoever seeks joy in God will always be joyful because God is forever.
(In Io. Ev. XIV, 2)