In the original creation of the world God made us perfect with the perfection of nature, which consists in our having everything due to our nature. But over and above what is due to our nature there were later added to the human race certain perfections that were solely owing to divine grace. Among these is faith, which is a “gift of God,” as is clear from Ephesians 2.8.
Thomas Acquinas (Exposition of Boethius’ De Trinitate, Question 3, article 1, reply to objection 2)