Montaigne explained in this work that total self-knowledge or mastery was nigh impossible. He reckoned that humans, being inside our own heads, can only see a portion of our experience and therefore only understand a small bit of it. If we could totally understand ourselves, we would be tantamount to God.
He did believe, however, that one could improve their self-mastery and begin to grasp more and more of oneself and one's environment. In fact, he set himself along this path personally in an attempt to try and enlighten himself totally. He laid out practical steps as to how he would achieve that, and he certainly became more self-aware, though it is debated how masterful he truly became in the end.
His steps achieve true knowledge of himself were the following: first, he decided that he must accept that he cannot know the true purpose and reason behind many things. The second step toward his idea of enlightenment is to focus on humanity's internal freedom.
This is integral to fully understanding and controlling oneself because it includes an understanding of what one cannot control—the exterior influences. Finally, he casts off inauthentic attitudes and mindsets and focuses purely on what is true and valuable.
In his Essays, Montaigne inquires about limits of human knowledge and self-knowledge. He says time and again that God is not fully knowable nor are we to suppose that we can reach complete self-knowledge. In particular, the thinker compares attempts at apprehending our own being to those at grasping water:
for the more you clutch your hand to squeeze and hold what is in its own nature flowing, so much more you lose of what you would grasp and hold. (book 2, chapter 12)
And though the philosopher’s approach can be termed skeptical fideism (a quest for knowledge and self-knowledge driven by faith but balanced by doubt), he does not reject reason altogether. Rather, he encourages us to test it and see what it is worth. At the same time, Montaigne defines man but negatively when the latter is viewed in the light of God’s perfections:
Thus is it that to God alone glory and honour appertain; and there is nothing so remote from reason as that we should go in quest of it for ourselves; for, being indigent and necessitous within, our essence being imperfect, and having continual need of amelioration, ‘tis to that we ought to employ all our endeavour. We are all hollow and empty (book 4, chapter 16)
Montaigne believes that the only way to locate and manifest one’s own self is self-reflection through introspection. Montaigne’s thought moves in three stages. First, he comes to the conclusion that we cannot really know true reasons of many things, including our own selves. Life is a totality of appearances, or “masks.” Second, Montaigne isolates man’s inner freedom as the sole truly human endowment from everything that affects it from without.
However, it is impossible to overcome this unauthentic reality completely. Yes, man is “hollow and empty”, but there is no other reality for the sake of which all appearances have been negated. The third stage in Montaigne’s reasoning is to integrate the negation of the unauthentic reality with an acceptance of each person’s relatedness to other beings:
there is nevertheless a certain respect, a general duty of humanity, not only to beasts that have life and sense, but even to trees, and plants. We owe justice to men, and graciousness and benignity to other creatures that are capable of it. (book 2, chapter 11)
As his thought progresses, Montaigne shows a more favorable attitude toward human nature. We need to consider its wants but, at the same time, we also need to balance this with reason. To trust your own nature is to find a way toward your true self, and this will contribute to its “amelioration.” Man’s goal is not to find an abstract truth but rather to agree to live through everything that his existence involves.
Michel de Montaigne wrote essays on a wide variety of subjects, yet he insisted that their subject was himself. More than that, he advocated that everyone seek self-knowledge, especially as humans are so prone to criticize others. This self-knowledge would help to temper, not to exacerbate, pride in one's own accomplishments.
Several essays elaborate on specific aspects. "On Vanity" and "On Moderation" explore these themes. Montaigne does not deny that he is vain; it is a basic human quality to be partly overcome by surrounding oneself with superior beings, both one's living contemporaries and the great thinkers of classical times. Aiming for self-mastery by restraint from overindulgence is recommended and, while laudable, a virtue that the speaker hesitates to claim for himself--that would be vanity.
In his longer essays that engage substantively with other philosophers, Montaigne argues for self-knowledge through faith rather than through reason. His dialogue with skepticism and modern proponents of rationalism, in which he refutes reason as superior to Christian faith, are laid out extensively in the "Apology for Raimond Sebond." Yet as he obviously is thoroughly schooled in their ways of thinking, he also reveals the strong attraction that skepticism exerts on him, and he comes across as revealing his own doubt as much as advocating for faith.