Question: On the 15th of Av, the following events took place in our world: the plagues of the generation that exited Egypt stopped; the ban on the marriage of the Benjamin tribe to girls from other tribes was lifted; the general ban on marriage between the tribes ceased to exist; the border guard between the northern and southern kingdoms was abolished, and so on.
Why did the elders revoke the laws of the Torah that prohibited mixing the tribes?
Answer: The fact is that there are laws that can be implemented during a certain historical period, and there are laws that are permanently in effect.
Until then, certain mutual corrections exist sequentially at different levels. That is, the right and left lines unite there separately, here separately, and by levels from bottom to top. Therefore, there are laws that are somewhat and somewhere partially canceled, and there are laws that are still preserved and will be canceled in the future.
From KabTV’s “Spiritual States. Day of Love—Tu Be-Av“