Some would say that religions are actually say the same things, even if they use different words and even if they think they are saying different things.
In this case the topic is no longer related to what they teach, but to their essence.
Does this describe what you mean?
All religions actually are the same in essence
One perspective on this topic is that religions may appear different and have different cultural trappings associated with them, but all religions are the same in their essence. Given the role of religion in history, culture ethics, and more, what an important topic! ...
All religions say the same things
A key component of all major world religions is that they teach a certain set of content. If you think that they all teach the same thing, what does their teaching agree on?