He goes on to say don't ask how this could be possible, (how could you be on such a lofty level where you are working every moment of your life and still recognize other simple folk as spiritually higher than you?) if you do it you will ultimately see that it is possible. But, I think maybe we can ask, how would one do it? He makes it clear that it's kind of a נעשה ונשמע - we will do and then we will understand, but perhaps we can still glean some meaning from his words, even if we aren't on the level where we get to see or understand, even if we have yet to begin this journey.
When a person goes against HaShem's mitzwoth, s/he is said to be the lowest of all creations. All of creation, no matter how mundane, are fulfilling the role for which HaShem created them, whereas this person is going against their assigned task.
You might want to argue that the animals, the insects, the fish, etc were not given free will! How can they get credit for fulfilling HaShem's wishes when they have no independent faculty to decide to stray from it? The most complete answer to this question is a resounding, because HaShem declared it so. But, perhaps we can glimpse at the smallest hint of a solution: There is a halachic principle that a person who fulfills a mitzwah which they are obligated to fulfill is greater than a person who fulfills a mitzwah that they optionally could perform, but were not outright required to perform. (גדול המצווה משאינו מצווה) This is counter-intuitive, one would think that a volunteer deserves more credit than someone who is required to do something? The Torah teaches us the opposite, kol haKavod to the volunteer, but the challenge to do something is much greater when you know you are obligated to do it. Even if you don't want to, you still have to. The volunteer only comes from a place of wanting to.
In the same way, perhaps, since the animals were commanded to act the way they do, and they continue to do so, they merit reward along the lines of those who are required to do so and do so. Even though they have no choice in the matter, they still may not want to do it but they still do it.
Similarly, people who go about their daily business with no awareness of HaShem or even really of their own actions, in a way can be compared to animals. (l'havdil) The question of their free will is almost a moot point. In that sense, they go about there business on the level of animals, in the automatic dance of nature. Therefore, they are always fulfilling the will of HaShem, giving no thought to whether they want to or not, without revolution or rebbellion.
True, the Tzaddik is pursuing HaShem and holiness and upholding HaShem's holy mitzwoth, but who is he to take on this job? If one (has v'shalom) wants to take upon himself this task for personal gain or respect, then one has become lower than the animals, lower too than all the simple folk. If one truly wants to serve HaShem, then he is confronted by his ego in numerous guises, his effort is always bent on eradicating his own self-interests. As long as he has any fleck or stain of self-interest, perhaps he can see himself as truly lower than the animals.
It's important even for us to take away basic lessons from this teaching. How often do we judge others harshly because of selfish reasons? How often can we remove ourselves from our deeply ingrained competitive nature and recognize that what we see as a failure in others is really not a flaw at all? If we were impartial, or better yet, if we were concerned for their well-being and success, wouldn't we be encouraging them and laughing about it a lot of the time?