The Six Books of Proclus on the Theology of Plato, Volume 2

For if it has an immutable and eternal essence, it proceeds from an immoveable essence. For that which proceeds from a moveable essence, is essentially changed in every respect. The cause, therefore, of every soul is immoveable. But if it proximately subsists from intellect, it is perfected by, and converted to intellect. And if it participates of the knowledge which intellect imparts to the natures that are able to partake of it; (for all knowledge is derived from intellect, and all things have their progression essentially from that to which they are naturally converted)—if this be the case, every soul proceeds from intellect.