Up until the establishment of the 'new covenant' prophesied about in Jeremiah 31, there was not provision for individuals to serve as both kings and priests at the same time. The Law covenant separated the roles into different tribes.
Not enough Jews accepted the Messiah to fill the full number of positions open. The is foretold to happen in Hosea 1:10 and reiterated at Romans 9:25,26; 2 Corinthians 6:18; 1 Peter 2:10.
God Law does stand forever, but when is he referring to the covenant specifically and when is he referring to torah' in a greater sense? Are people confusing torah' with mishpat' (judicial decision/judgement) and mitswah' (commandment)?
The Law Covenant itself was bilateral. Meaning it could be broken and the other party would no longer be obligated to keep it. But the torah', being related to the verb yarah' can also mean "direction,teaching,and instruction," and not to the Law Covenant exclusively, these things from Jehovah do endure forever, as He will always be our Lawgiver. (Isaiah 33:22)
(Granted I have not looked up the scriptures showing the bilateral nature of the Law Covenant to cite here. I am typing between obligations.)
Fortunately, a fair number of churches have realized that to claim that the Law and Covenant could supposedly be terminated by God after He promised He wouldn't, that this would basically make God a liar. What they have done is to now believe that the "new covenant" was added to the "old covenant", which makes far more sense and doesn't turn God into one who breaks His promises.
I believe I posted the messianic verses on this thread, but if I'm confusing this with another thread, let me know and I'll post them again. Also, you can access the 613 Laws and where they're found in Torah at the Judaism 101 website if you're interested.
BTW, God at a couple of times in the Tanakh does threat to back out of the Covenant if we don't straight up our act, but then He states that He wouldn't do that. Instead, another covenant can be found In Ezekiel that goes forth from there whereas the final judgement will be done on a
personal scale, not on the entire society. IOW, if I screw up, all Jews will not be judged by that, but I will be judged. This carries over into the Christian scriptures, as personal judgement is what's promised.
However, let me make it also clear that if I screw up, this may have a negative affect on both other Jews and non-Jews, so it's not like I'm living in some sort of bubble. .