help me understand this OT and NT stuff

[Minimalist]

The OP raises a decent point, not about which of these two piles of shit should be followed but why is the OT even appended to the NT in the first place.  The earliest, more or less "complete" bible we have, the Codex Vaticanus from the mid 4th century includes the Septuagint.  We are told by xtian sources that Marcion in the first xtian canon c 140 AD had nothing good to say about yhwh or any of his bullshit.  Thus, in the two centuries between Marcion and the Codex Vaticanus somebody decided to tack on all the jew-shit.  I have seen speculation that the creators of proto-orthodox jesusism wanted to give their new cult a sense of antiquity with the idea that "new religions" were not to be taken seriously.  Can't recall where I read that, though.