Et omnino debes ut cum uolueris imaginari has substantias, et qualiter tua essentia est diffusa in illis et qualiter est comprehendens illas, ut erigas tuum intellectum ad ultimum intelligibile et ut purges eum et mundicifes ab omni sorde sensibilis et ut expedias illum a captiuitate naturae et ut accedas cum ui intelligentiae ad ultimum quod tibi possibile est apprehendere de certitudine substantiae intelligibilis, donec quasi denuderis a substantia sensibili et fias quasi ignarus eius. et tunc quasi includes totum mundum corporalem intra tuam essentiam et pones eum quasi in uno angulorum animae tuae; quia quando hoc feceris, tunc intelliges minoritatem sensibilis secundum magnitudinem intelligibilis.
"And when you want to imagine these [spiritual] substances, and how your essence is diffused in them and how it comprehends them, you ought to lift your intellect to the ultimate intelligible and purge it and purify it from every coarse sensible thing and loose it from the captivity of nature, and so that you may draw near with the power of intelligence to the ultimate thing which it is possible for you to apprehend of the certitude of intelligible substance, until as it were you may be stripped of every sensible substance and may be as it were unaware of them. And then as it were you will include the whole corporeal world within your own essence and will hold it to be as it were in one corner of your soul; for when you do this, then you will understand the littleness of the sensible world compared to the magnitude of the intelligible."
Avicebron, Fons vitae Tr. III.56.