According to Rashi, this applied when the kohanim were in a state of ritual defilement. At such times they had to observe restrictions and not think, as Sforno points out, that they were above the law and could do whatever they fancied.
No priest or leader was or is too important to be subject to the law. In modern times the lesson may be one for those who say to a police officer, “You can’t book me – I’m a VIP!” Or those who say, “I’m allowed to rort the system – I’m a high flyer!” Or maybe, “I’m a star, and stars don’t have to be faithful to their spouses!”
Trading on your status, exploiting your eminence and rank – it is an insult to society and its mores and it degrades the concept of leadership. The moment a leader becomes too big for his or her boots is the moment to give up, step down and go back to the ranks.