Some of the philosophers in ancient Greece included fragments of the reality of God in their words. While certainly not anything like how God is revealed to us through the prophets and the Bible, fully, clearly and absolutely, it is amazing to see that even the pre-Christian pagan philosophers managed to contemplate and approach God through the God given gift of common logic or simply the gift of reason.

http://lexchristianorum.blogspot.com/2010/03/st-justin-martyr-spermatikos-logos-and.html

An excerpt from the blog above presenting the view of St.Justin the Martyr on the same issue:

This divine principle in man had an intimate relation with the Divine Logos, the Word of God. "In every man," St. Justin Martyr believed, "there is a divine particle, his reason, which at least before Christ's coming was man's best guide in life." Goodenough, 214 (citing Ap. II 10.8) It is man's burden to live in accordance with reason, μέτα λόγου (meta logou), and not against or without reason, ἄνευ λόγου (aneu logou). It was thus living in accord with right reason, which was participation in divine reason, that was man's fundamental law.