We do not often see philosophers and theologian on the modern list of canonizations without them also being Doctors of the Church. He was a genius of thought and it is the power of John's theology that draws me, the power of Christ's love. In love is absolute freedom; we only grow in freedom as we grow in love. This alternate way of looking at the will was in answer to the rising idea of determinism. He took on the notion of determinism versus free will by thinking about it like this: if I begin to do something, and you asked me to stop, how can I stop if all is completely determined - it must play itself out to the end. I must have some sort of mechanism that allows me to go against determinism. But freedom was tied to love, not to some arbitrary notion or determinism. God is the foundation of all things but we may begin to know Him through our experiences, before we understand Revelation. Human reason has boundaries but we can begin to understand the perfection that is God...but I begin to go down a rabbit hole here, discussing the man's thoughts rather than his life.
What makes him a saint? His thought? His credentials as a teacher? Ultimately I think it is because he took St. John's definition of "God is love" (cf. 1 John 4:7-12) to heart. The wonder of the Incarnation was not required as payment for sin; it was the free willed expression of God’s love through all of eternity and was a result of God’s desire for union with His creation. So our redemption by the cross was not an appeasement of God’s anger or some sort of compensation for some bruising of God’s majesty caused by our sin but was part of that expression of love. Love is not revenge or payment.
God’s love should call forth from us an equal loving response: “I am of the opinion that God wished to redeem us in this fashion principally in order to draw us to his love.”
O Lord, our God, Catholics can infer most of the perfections which philosophers knew of you from what has been said. You are the first efficient cause the ultimate end, supreme in perfection, transcending all things. You are uncaused in any way and therefore incapable of becoming or perishing; indeed it is simply impossible that you should not exist, for of yourself you are necessary being. You are therefore eternal, because the span of your existence is without limit and you experience it all at once, for it cannot be strung out in a succession of events. For there can be no succession save in what is continually caused, or at least in what is dependent for its existence upon another, and this dependence is a far cry from what has necessary being of itself. You live a most noble life, because you are understanding and volition. You are happy, indeed you are by nature happiness itself, because you are in possession of yourself. You are the clear vision yourself and the most joyful love, and although you are self-sufficient and happy in yourself alone, you still understand in a single act everything that can be known. At one and the same time you possess the power to freely and contingently will each thing that can be caused and by willing it through your volition cause it to be. Most truly then you are of infinite power. You are incomprehensible, infinite, for nothing omniscient or of infinite power is finite . . . Neither is the ultimate end, nor what exists of itself in all simplicity, something finite. You are the end, nor what exists of itself in all simplicity, something finite. You are the ultimate in simplicity, having no really distinct parts, or no realities in your essence which are not really the same. In you no quantity, no accident can be found, and therefore you are incapable of accidental change, even as I have already expressed, you are so in essence. You alone are simply perfect, not just a perfect angel, or a perfect body, but a perfect being, lacking no entity it is possible for anything to have. Nothing can formally possess every perfection, but every entity can exist in something either formally or eminently, as it does in you, O God, who are supreme among beings, the only one of them who is infinite. Communicating the rays of your goodness most liberally. you are boundless good, to whom as the most lovable thing of all every Single being in its own way comes back to you as to its ultimate end.
-- Treatise on God as the First Principle