Back to the OP, when people say we shouldn’t try to understand the reason, that is as a response to doing things because of your understanding.
לכל תכלה ראיתי קץ, רחבה מצותך מאד.
Although obviously there is a reason for each Mitzvah, we don’t, and cannot, understand the full reason even for a relatively well-understood Mitzvah.
Most of Torah Shel Baal Peh is about learning the exact classification of a Mitzvah and therefore how it applies. We can then draw an understanding built upon its Halachos.
And so, it is important to realize first and foremost that your motivation to act is because Hashem commanded you to do so. Then, on top of that, the more you understand about the Mitzvah accomplishes more.
But it is important never to think that the reason at hand is the reason. I know of a certain Tzaddik who preferred as a Baal Toke’ah someone who didn’t know the Kavanos of the Arizal. This way he can’t mess up.
So, think of it as a base, which is about being an Eved Hashem, and on top of that many understandings, meditations, and achievements.