His definition of piety (1:41)
His thoughts on Christian Hedonism (yes, another anachronism; Ibid)
"Nay, unless [men] establish their complete happiness in Him, they will never give themselves truly and sincerely to Him."
The purpose of knowledge of God (Ibid)
"Rather, our knowledge should serve first to teach us fear and
reverence; secondly, with it as our guide and teacher, we should learn to seek every good from him, and having received it, to credit it to his account."
On understanding providence (1:21)
"Therefore no one will weigh God's providence properly and profitably but him who considers that his business is with his Maker and the Framer of the universe, and with becoming humility submits himself to fear and reverence."
Finally, my favorite among favorites - after almost thirty pages of argumentation and explanation of the doctrine of providence (sovereignty), his closing sentence reads as follows (1:225):
"In short, not to tarry any longer over this, if you pay attention, you will easily perceive that ignorance of providence is the ultimate of all miseries; the highest blessedness lies in the knowledge of it."
He wrote all this in his late twenties. Is it any wonder the man's writings have lasted roughly 5 centuries?