It is easier to grasp the mystery of evil if we focus on the angelic world mentioned in the Bible.
It is worth remembering that it wasn’t just the Queen of Angels who was subjected to a radical spiritual choice (Fiat, let it be done, or Non serviam, I will not serve), but the angelic spirits themselves were put to the test. With a few quotes from Scriptures, Saint Thomas Aquinas teaches that the angels were created in a state of grace, but without yet seeing God.
From the moment of their creation, the angels became aware of their own perfection, which brought them great joy and made them praise God, but they were soon called by their Creator to detach themselves from that beautiful initial state to rise higher, above themselves, to a supernatural destiny beyond what they could have imagined: to contemplate God face to face in an eternal and jubilant ecstasy of love (Rev 5:11).
Together with theologians like Saints Augustine and Gregory, Saint Thomas Aquinas also thinks that, in the same moment that they were thus called to Divine Life, God also revealed to them their future mission and place in the supernatural order, especially their dependence on the future Incarnate Word and His Mother, full of grace yet a simple human. For their pure spirit, this certainly constituted a test, for it was tantamount to asking them to leave a reality beautiful and good in itself in order to submit to another paradoxical order that could only hold its coherence from Divine Love going beyond all the expectations of a created nature.
In order to adhere to such a plan, the angels had to abandon their limited judgment and trust their Creator, in an act of supernatural love producing merit, whereby they were given an opportunity to cooperate freely with God in attaining their destiny of eternal happiness. Some mystics have maintained that at that moment of choice, the angels were strengthened in their act of abandonment to God by perceiving a glimpse of the immaculate being of their future Queen, at once so humble and so close to the Most High.
Adapted from: Spiritualite Chretienne