Quite possibly the most important book one could read outside of the Bible itself. It's everything you should know about Christianity and the tenets of the true Orthodox faith, explained in all detail and godly humility. While it's directed at those entering or within the Armenian Apostolic Church (there's a portion on the rich history of the church in Armenia), this catechism can and should be read by anyone interested in developing and enriching their faith in Christ, from the newly saved to the seasoned believer. It was an especially invaluable resource to me as a longtime Protestant who converted to Orthodoxy.