More often than I can count, I've been asked to recommend books that I found useful as I contemplated becoming Orthodox. More often than not, the inquirer is looking for only a few noteworthy books. Moreover, the inquiry presumes that one can read his way into the Church. One can't. For the Church is not an academy or library; rather, she is a living organism, a body. Therefore, what is key is not knowledge but relationship; and not the letter, but the Spirit.
Nevertheless, knowledge and letters (i.e., books) are not unimportant. For they help clarify the relationship and articulate the organism. Or, to say it another way, while faith does not require understanding, understanding forms and informs faith.
As I've pondered the question in order to give a reasonable and cogent answer, I have reviewed the past five years and determined that there certainly are many books that have been most helpful. But I keep coming back to three in particular--the three that I am certain formed my understanding of and stoked my desire for the Church. These three are: the English Missal, the Anglican Breviary and daily selections of homilies from the Church Fathers.
During the five years leading up to my chrismation, I daily read these three books as a celebrated daily Mass at the Lutheran congregation that I served. During that five I period, I gradually drifted away from trying to "Lutheranize" these texts by careful editing (as had been my arduous practice), but rather to let the propers, Psalms, hymns, prayers, and fathers speak for themselves, earnestly endeavoring to understand their context while determining that I was not smart enough to correct self-perceived mistranslations or accretions but humbly attempting to hear and learn from these texts. In Lutheran parlance, I no longer exercised a magisterial but a ministerial use of reason concerning the liturgy and the fathers.
I am convinced that this use of these texts, more than anything else, led me in time to the understanding that, while I miraculously and wondrously exercised the grace of the Holy Spirit through preaching and the Sacraments, I did so outside of the Church--much like the man in Mark 9.
As I stated above, along the way many other books, articles and discussions were helpful. But these three texts--the Scriptures in the liturgy, the Scriptures in the breviary, and the Scriptures interpreted by the fathers--were, for me, the most formative in my "journey."