The Holy Spirit inspired them to write to Yehova’s elect!
There is nothing added to goad anyone else into understanding.
Enduring does not require any more than a true commitment to Yeshua. Some make that commitment, and some do not. He only wants those that do. Obedience is not “works based salvation,” it is the result of love. Some have it, some do not.
Your post makes it sound like you resent having to be obedient; I hope that is not so.
100 to go