The film, which has been described as Director Martin Scorsese's passion project, tells the story of two 17th century Jesuit priests who travel to Japan in order to locate their missing mentor and spread Catholicism.
Garfield, who is most famous for portraying Spiderman, plays the role of one of the priests and in preparation, took part in the Spiritual Exercises of St Ignatius Loyola.
The Exercises require those taking part to retreat for a number of weeks to discern the will of God in their lives.
Part of the process is said to include prayers and mental exercises which take the participant to different parts of the life of Jesus.
Speaking of his experiences to the US magazine National Catholic Review, Garfield said: "There were so many things in the Exercises that changed me and transformed me, that showed me who I was...and where I believe God wants me to be."
When asked what the most interesting aspect of the Exercises was, he said: "What was really easy was falling in love with this person, was falling in love with Jesus Christ. That was the most surprising thing."
"That was the most remarkable thing...falling in love, and how easy it was to fall in love with Jesus."