In general, your humble author shies away from discussing the “reasons” for mitzvos, preferring to focus on the “lessons.” There are numerous reasons for this.
The Torah rarely gives reasons for the mitzvos. In one famous instance, it does. Deuteronomy 17:16-17 says:
“The king shall not gather himself many horses, which would cause the people to return to Egypt in order to get horses, since G-d told you not to return that way again. Nor shall the king many wives for himself, as this will cause his heart to turn astray…”
Regarding these mitzvos, the reasons are overtly stated. Nevertheless, King Solomon, the wisest of all men, was able to err in them. The Talmud in Sanhedrin (21b) explains that Shlomo (Solomon), knowing the reasons, said, “I can gather many horses and I’ll just make sure the people don’t return to Egypt; I can gather many wives and just be careful not to turn astray.” Nevertheless, the people did return to Egypt to engage in the horse trade (see I Kings 10:29) and some of Shlomo’s many wives built idols in his household, for which he was considered responsible (see I Kings 11:4). So knowing the reasons for mitzvos can be dangerous, as it tempts one into thinking that the reasons don’t apply.
On the other hand, the Talmud in Brachos (33b) seems to disapprove of ascribing motivations to mitzvos whose reasons are unstated. It says that we should silence one who adds the words “Your mercy is even on the bird’s nest,” referring to the mitzvah to shoo away a mother bird before taking the young from the nest (Deuteronomy 22:6-7). The Gemara asks the reason for the objection and it answers along the lines of, “Who are we to decide that the reason for this mitzvah is G-d’s mercy? The reason is that He said so!”
So there are two motivations for us to avoid defining the reasons for the mitzvos: (1) it’s presumptuous and (2) to know the reasons for the mitzvos can lead one to focus on the reason to the exclusion of the behavior that G-d wants from us. (A famous example is that those who attribute kashrus to health reasons would argue that modern medicine renders those mitzvos moot, G-d forbid. If the reason for Shabbos is to rest, driving is more restful than walking, etc.) However, this position, is not universal.
The Rambam understands the objection of the Talmud differently. He says in his Commentary on the Mishna (Brachos 5:3) that the reason we silence one who ascribes the mitzvah of sending away the mother bird to mercy is because it’s simply inaccurate. “It’s not so,” the Rambam writes. “If it was because of mercy, then we would never be permitted to sacrifice animals at all. Rather, (sending the bird away) is a mitzvah we have been instructed without being given a reason.” The Rambam does not, however, object to analyzing the reasons of the mitzvos per se. He writes in Moreh HaNevuchim (The Guide for the Perplexed) 3:48, “It is one of two opinions of the Sages to say that there’s no reason for the mitzvos other than that G-d told us to do them. We, however, subscribe to the second opinion.” And you’ll see that Rambam, Nachmanides and the Sefer HaChinuch, among others, do discuss the reasons for the mitzvos, even for those not stated by G-d in the Torah.
Even the Rambam, however, treads carefully in this area. Recognizing the trap into which King Solomon fell, he sates, “If we knew the reasons underlying all the mitzvos, we would find excuses to do away with all of them… saying that G d only commanded one thing and forbade another because of such-and-such reason, therefore we will safeguard the reason and not have to do the mitzvah… This is why G-d did not reveal the reason behind most mitzvos, and the reasons for many others are beyond the comprehension of the average person…” (This appears at the end of his discussion of the aforementioned mitzvos of the king, which is the last mitzvah in the Rambam’s Sefer HaMitzvos – Negative Mitzvah #365.)
And so, despite our usual hesitancy to do so, we shall use the term “reasons” when discussing the mitzvos, at least insofar as we are citing the reasons stated by our authorities. Other observations, especially our own, will be considered lessons that can be derived from the mitzvos.