Writing a thesis statement on the topic of "Christianity" is easy and difficult at the same time. It's easy because the topic is so broad that you could pick just about anything involving Christianity. The difficulty is that the topic is so overwhelmingly wide that the thesis could prove to be useless because it is far too broad.
The purpose of a thesis statement is that it makes an argument that you intend to support and try to prove correct. A thesis statement is not a statement of fact. For example, "Christianity is one of the world religions." That's not a thesis statement because it isn't making an argument. It's stating a fact.
It's up to you what you want to argue about Christianity. You could argue that it is the one true religion. You could argue that its beliefs are completely false. You could argue that Christianity is the most unique religion available to people. None of those are incontrovertible facts. They are statements of opinion that now need to be supported in the body...
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