We have an Old Testament and a New Testament.
Jesus did have the ability to change the rules, and He did.
I believe that Christianity must pay attention to tradition AND to Scripture. From the very EARLY Church, Christians understood that the “Sabbath Day” was now Sunday and not Saturday.
The problem I have, with supposedly “Christian” Faiths, who go directly to the text of Scripture is this:
They are using Scripture in a way it was not intended, by the very people who WROTE the documents. Much of Scripture was an oral history. Much of it was a rebuke of certain practices, when a group went astray. Never, in the New Testament, can you find a complete guide to what Christian Life was like, in the Early Church. The very people who WROTE Scripture expected those habits and traditions to be passed on, just as the other ORAL traditions had been passed on for years, before being put to writing.
So, that something can NOT be found in the Bible is much like saying that the “users guide” for your car, does not contain a map to Buffalo, and therefore, you are NOT allowed to drive to Buffalo. (That, of course, is not what your “users guide” intended.) Also, I understand your charitable view towards others of faith, and I mostly share that view. However, the "Millerites" who are now in the Jahovah's Witness and 7th Day adventist ranks are among the most hostile on the planet, towards other faiths. Their literature is full of hate and lies and historical inaccuracies, as well as some crack pot theories. They do not allow their members to explore other faiths, or to have much contact with other faiths. Understandable, since any Baptist, Catholic, Evangelical or member of most other faiths can poke holes in the Millerite theories.
When I was a Baptist, the best part of being one is that Baptists never recognize each other at the liquor store.