Proponents of the view that Washington was a Christian can cite the facts that Washington made frequent references to God in his speeches and writings (although he often used various titles for God, rather than simply the word God) and was a fairly regular churchgoer. On the other hand, proponents of the view that Washington was a deist note his failure to make an unequivocal declaration of Christian faith (even on his deathbed) and argue that his use of titles for God like "Supreme Ruler of the Universe" is more consistent with the practice of deists. Numerous articles and books have been written on the subject and most likely will continue to be written. Nonetheless, in recent years, it seems that among most historians the notion that Washington was a deist of some sort has become conventional wisdom. For example, this is the position taken by well-known historian Joseph Ellis in his popular account of the early years of the American republic, Founding Brothers.
I do not intend in this posting to discuss my own beliefs about this controversy. Given what reading I have done on this matter, I think it is fair to say that if one looks at all the relevent historical evidence, it is difficult to come to a definite answer. Instead, what I would like to do is to express some thoughts about why this controversy continues to be so heated.
I would argue that to a large extent the argument about Washingotn's religious beliefs is really a reflection of a conflict within modern American society. In the current controversaries about such issues as abortion and homosexulity, we can see two dramatically different perspectives--that of theologically conservative Christians (many of them Protestant evangelicals but also including many Catholics, joined by some traditionalist adherents of other religions like Judaism and Islam) and that of those who have, to one extent or another, rejected traditional Christian beliefs, ranging from theologically liberal "Christians" to agnostics and atheists. Moreover, both sides have not only contrasting views about what kind of country the United States should be in the present, but also about what kind of country it was in the past. This is because in some sense, both sides are anxious to appropriate the prestige of the great figures of the past in support of their views about what present-day America should look like. Hence the debates about whether the U.S. was ever a "Christian nation" and the extent to which the founding fathers were Christians.
This conflict shows little sign of going away any time soon, as the ongoing political and legal struggle over so-called same-sex marriage demonstrates. Consequently, I think it is safe to predict that the controversy over what Washington believed will not abate any time soon either, barring the emergence of incontrovertible historical evidence in support of one view or the other. Nevertheless, regardless of what the truth in this matter is, I would like to suggest that Washington, the "indispenable man," despite the very human flaws that he had, is quite worthy of our admiration today and of the admiration of generations to come.
Portrait of George Washington by Gilbert Stuart from mountvernon.org