Pascal's understanding of amour-propre, or self-love, owes a great deal to St. Augustine. For Augustine, self-love is a consequence of the Fall, when man's original ancestor Adam defied God by eating of the fruit of the Tree of Knowledge. Though Pascal's thought in the Pensées is inevitably much more fragmented than Augustine's it's nonetheless possible to discover a remarkable degree of consistency in his understanding of amour-propre.
Like his famous predecessor, he sees it as a theological concept equivalent to the sin of pride and associated with concupiscence, or strong sexual desire. According to Pascal, amour-propre is fatal to the health of the soul. In fact, it can destroy it completely by separating it from God, its only true source of happiness.
God makes the soul aware that he is its sole good; that in God alone is it possible for the soul to find peace. At the same time God fills the soul with a hatred for all that holds it back from loving God with all its might. In other words, God makes the soul aware of the damaging presence of amour-propre which only God himself can cure.
Pascal's withering attack upon amour-propre is part of a wider critique of man's arrogant usurping of God's place at the center of the universe. Because man is the center of his own universe, he automatically thinks that he's at the center of the universe as a whole. Such blatant egoism leads to a desire to dominate and control others, with disastrous consequences. Though an inevitable component of fallen man's sinful condition, this innate capacity for tyrannizing others must be overcome if the soul is to find its rest in God.