You appear to have difficulty understanding English.
The Aztec religion is a religion and is therefore protected under the Constitution.
This does not mean it protects their human sacrifice practices.
IOW, the Constitution absolutely protects any and all religious belief. It does not protect all religious practices. While somewhat greater latitude is given actions that are religious in nature, extreme practices such as human sacrifice are not protected.
IOW, beliefs (thought) are protected, actions not so much. I don’t see why this is difficult to understand.
That is precisely the key distinction. “Thought crime” in any form is antithetical to any free society, however society has both a right and a duty to establish norms of public behavior for the common good.