Harper Lee's "Go Set a Watchman" just came out, but the book's title has been around for much longer.
The phrase "Go Set a Watchman" is found in the Bible. It comes from the Book of Prophet Isaiah, in the King James Version.
Lee is hardly alone. Plenty of other authors have used the Bible as inspiration, too.
More recently Lois Lowry's "Number the Stars" comes from Psalm 147:4, which reads, "He determines the number of the stars and calls them each by name."
And the book-turned-movie, "My Sister's Keeper" falls under this category too. It takes a slight twist on the Genesis passage, changing my brother's keeper to sister's. (Video via Warner Bros. / "My Sister's Keeper)
Of course, just because a book uses the Bible as its inspiration, don't confuse it for being religious.