The little similarities go on. Both books present the media as corrupt or easily corruptible. The Left Behind tribulation takes seven years; so does Hogwarts'. Carpathia takes the form of a snake; Voldemort takes the form of a lizard, and Harry is able to tap into the evil world by speaking snake (parseltongue). And in both, the good guys bear a special "mark"—on their foreheads!—that protects them.
Finally, they both have a theology. It's not, as one might expect, that Left Behind is Christian and Harry Potter pagan, but rather that Left Behind is Protestant and Harry Potter is Catholic. One of the chief theological arguments between Catholics and Protestants has been over whether salvation is earned through faith or by good works. In Left Behind, the only thing that matters is faith in Jesus. Steele explains that church leaders had led so many people astray because they merely "expected them to lead a good life, to do the best they could, to think of others, to be kind, to live in peace. It sounded so good, and yet it was so wrong. How far from the mark!"
While everything is pre-ordained in Left Behind, in Harry Potter, by contrast, Dumbledore explicitly tells Harry that even though he carries some of the essence of Voldemort in him, he has the power to do good because he has the power of choice.
In that sense, despite their similarities, at their hearts the two series are different in a fundamental but not obvious way. Left Behind is fatalistic; Harry Potter sees outcome determined by individual actions. Both provide a roadmap for how to live a good life, but in one case the key is morality, and in the other it is faith.