In the beginning of Mesillas Yesharim the Ramchal writes:
When you look further into the matter, you will see that only connection with God constitutes true perfection, as King David said (Psalms 73:28), “But as for me, the nearness of God is my good,” and (Psalms 27:4), “I asked one thing from God; that will I seek – to dwell in God’s house all the days of my life…” For this alone is the true good, and anything besides this which people deem good is nothing but emptiness and deceptive worthlessness. For a man to attain this good, it is certainly fitting that he first labor and persevere in his exertions to acquire it. That is, he should persevere so as to unite himself with the Blessed One by means of actions which result in this end. These actions are the mitzvos.
The goal is connecting deeply to G-d and the path to achieving it are the mitzvos. The sefer Mesillas Yesharim itself is focused on doing mitzvos progressively better to achieve their intended goal.
Let’s take the first 2 lines of Shema as an example. The halacha states that we have to pay close attention (have kavanna) to what we are saying for the first 2 lines. If we don’t do that, we won’t get the full benefit from saying the Shema and it will not help us get closer to Hashem to the degree that it could.
It takes a reasonable amount of effort, just to observe the mitzvos, so we often feel accomplished just from the fact that we are observant. If we take a little step, and do mitzvos with intention and with a focus on connecting to Hashem, we will get much more out of them and will can avoid the frustrating plateauing state.
Someone might choose to write a lot more on that subject. FWIW, I made Rava’s argument that mitzvos not only are the means to sanctity (leaving how we define that aside), but if one doesn’t keep their eye on the goal, they could end up the means to something self-destructive.
http://www.aishdas.org/asp/tools-and-goals
(Thanks again for your earlier link to the essay.)
Thus one can’t simply just “follow the Shulchan Arukh” and take it for granted that the mitzvos and learning will get you to the goal. Without exercises like this one, a person could end up deluding themselves into thinking they’re good Jews because (eg) they say Shema slowly and never miss it 3-1/2 times daily, meanwhile heading for decay.