Moshe commanded Aharon how to light the Menorah in the Mishkan, including certain nuances about how it had to be done, the steps taken to properly prepare it, and the attention to detail required.
The Torah tells us, “And Aharon did so.” Rashi says, “This teaches the praise of Aharon that he did not change.”
The commentaries famously discuss why we would think Aharon would change and veer from what he was instructed. Simply put, after one does something for a long time, he considers himself an expert, and may come to “improve” the process.
Aharon was humble enough to realize that when it comes to fulfilling Hashem’s commandments, we cannot improve on them, though we can beautify them.
On a different note, Aharon didn’t change refers to his attitude. He was as excited and thrilled after thirty years as he was the first day he did the job. And this is praiseworthy.
What it tells us is that Aharon made a conscious effort to find the joy and excitement in lighting the Menorah each day.
He may have had to psyche himself up, and induce that excitement, but he did it because he knew that is how we are supposed to serve Hashem.
