PhilosophyQuotes:

"Of all human pursuits, the pursuit of wisdom is the more perfect, the more sublime, the more useful, and the more agreeable."

"Those truths are self-evident which are recognised at once, as soon as the terms in which they are expressed are known."

"Everything is by its own existence. Whatever then is not its own existence does not of itself necessarily exist. But God does of Himself necessarily exist: therefore God is His own existence."

-Thomas Aquinas (1225-1274), Summa Contra Gentiles : God

Aquinas' Summa Contra Gentiles : God is available online at Amazon.com.