In his introduction to Pirkei Avot, the Rambam distinguishes between those mitzvot which we are to observe because we want to and those we should observe because we have to. When it comes to what we might call the ethical mitzvot of the Torah we should observe them because it is the correct thing to do, period. The fact that G-d may have commanded them is irrelevant – we are to avoid stealing because it’s wrong, not because G-d said so. G-d’s commands in ethical mitzvot are needed only for those who would have violated them if not for the command of G-d.
Those mitzvot which have no obvious ethical reasoning, and which one would never have come up with on one’s own, are to be observed because, and only because, G-d has so commanded. We refrain from pork not because there is anything inherently wrong with eating pork – one can eat pork on Yom Kippur and be the finest of human beings – but because G-d instructed us such. “Man should not say, 'I do not want to eat meat together with milk; I do not want to wear clothes made of a mixture of wool and linen; I do not want to enter into an incestuous marriage', but he should say, 'I do indeed want to, yet I must not, for my Father in Heaven has forbidden it'" (Introduction to Avot, chapter 6).
Throughout sefer Shemot it is G-d who takes centre stage with the Jewish people having been most passive. G-d brought the ten plagues, passed over our homes, split the sea, gave food from heaven and water from a rock. Save for putting blood on the doorpost, the Jewish people did little more than complain. To be fair, that is exactly what one should expect from a group of slaves. The fact that these slaves were willing to give up their “fish, leeks, melons and cucumbers that they ate for free” (See Bamidbar 11:5) – something our Sages assert the overwhelming number of Jews were not willing to do – and follow Moshe to a barren desert was a great act of enormous faith. They were not yet free of their slave mentality and thus not yet ready to enter the land. There was a long learning curve ahead. G-d fully understood and did not get angry at the people - until they built the golden calf.
But if up until G-d had taken care of the needs of the people, slowly but surely the Jews needed to be weaned from their dependence on G-d. Once they would arrive in the land, life would look very natural – so much so that they would need constant reminders that G-d was in their midst.
That reminder was to begin with the building of the Mishkan. “And you shall make for me sanctuary and I shall dwell in your midst” (Shemot 25:8). And it would be the Jewish people who would build the Mishkan.
It is through the building of the Mishkan that we fully actualized our divine image. G-d created the world so that man could dwell in it, and we reciprocate by building a home where G-d can dwell. That the creation of the world and building the Mishkan are intertwined is reflected in the notion that the laws of shabbat – the last act of creation – are derived from the Mishkan.
But unless one builds it because one wants to, it will have little meaning. “Tell the Israelite people to bring Me gifts; you shall accept gifts for Me from every person whose heart is so moved”. Worshipping G-d is of little value if it is forced. Forcing people to observe Torah does little more than turn people off of Torah. Hence our Rabbis teach that it is forbidden to rebuke a fellow Jew if the rebuke will be ineffective (Yevamot 65b). The mere suggestion that one needs to refrain from, say, eating chametz on Pesach is often the catalyst for the person to do exactly that.
“Rachmana liba baei, G-d desirers the heart” (Sanhedrin 106b). Our Sages teach that there are 248 positive Biblical mitzvot, corresponding to the limbs of the body. It is the heart that provides oxygen so that the body can survive and function. It is our duty to demonstrate the beauty of Judaism, beginning with the recognition that all are created in G-d’s image, that we are be models of integrity; “full of mercy, a sense of shame and doing acts of kindness” (Yevamot 79a). If we model such behaviour we will succeed in bringing the hearts of many closer to Torah.
 It is true that the ethical demands of the Torah often extend beyond what we may have thought on our own but this should have little bearing on why we keep these mitzvot.
 It is fascinating the Ramban includes arayot, sexual sins, as a law one should want to violate – if not for G-d’s command. In other words, there is no ethical or moral wrong with two consenting adults being intimate with each other. It may be unholy, but it is not inherently immoral and is forbidden only because of divine decree.This is something to keep in mind as the Orthodox community struggles with its relationship with the LGBTQ community.
While the Rambam does not explicitly say so, presumably he would agree that adultery, a heinous sin against one’s fellow man, is inherently immoral and hence would not fall under this category.