I think it's interesting that the most prominent existentialist thinkers have tended either to be passionately devout Christians such as Kierkegaard and Dostoyevsky, or emphatically atheist like Heidegger, Nietzsche and Sartre, and yet, apart from the specific question of God, their points of view and philosophical arguments harmonize quite well.
I think those two Christian existentialists, Kierkegaard and Dostoyevsky, are also the last... I was going to say, "the last Christians whom non-Christians generally consider to be great thinkers," but of course that's not true. Since Dostoyevsky there have been Eliot and Yeats and Karl Barth -- I don't know if a lot of non-Christians actually know and admire the work of Karl Barth, but I'm giving him the benefit of the doubt -- and Kazantzakis and a few others. Still, if you look at the number of Christians in the Western Canon, around the mid-19th century they very suddenly shrink from a torrent to a dribble.
One never knows, of course, how many of the earlier torrent didn't actually believe in God or Christ, but merely wished to avoid persecution for speaking clearly and sensibly and publicly on the subject of religion. As far back as the 17th century, Spinoza and Hobbes expressed themselves in about as clearly an atheistic way as was possible without endangering their lives and limbs. Even so, Spinoza was formally excommunicated from the Jewish community in Amsterdam. They had a formal ceremony in the Amsterdam synagogue, in which, according to Bertrand Russell, who seems to me to have been pretty good at getting the details right, Spinoza, was
"cursed with all the curses in Deuteronomy and with the curse that Elisha pronounced on the children who, in consequence, were torn to pieces by the she-bears." -- A History of Western Philosophy, 1946 & 1961, p.552.
According to Wikipedia, this is a translation of a preface to the community's ban, originally written in Portugese:
The chiefs of the council make known to you that having long known of evil opinions and acts of Baruch de Spinoza, they have endeavored by various means and promises to turn him from evil ways. Not being able to find any remedy, but on the contrary receiving every day more information about the abominable heresies practiced and taught by him, and about the monstrous acts committed by him, having this from many trustworthy witnesses who have deposed and borne witness on all this in the presence of said Spinoza, who has been convicted; all this having been examined in the presence of the Rabbis, the council decided, with the advice of the Rabbi, that the said Spinoza should be excommunicated and cut off from the Nation of Israel.
All of Spinoza's works were also placed on the Catholic Index.
So far I have not been able to find out what, if any, actual impact the bans by the Jews and the Catholics had on Spinoza's life.