In Anselm of Canterbury (1033-1109), we encounter one of the finest minds in the history of Christian thought. As bishop, he fought the king of England over the church’s right to appoint people to ecclesiastical offices. As a monk, he stood out among his fellow Benedictines. As a pastor, he was revered by those he was called to serve. And as a theologian, he explored every nook and cranny of the church’s teachings using the fiercest logic. On this day in the year 1093, he was consecrated as the archbishop of Canterbury.

He was born to a noble family in Aosta, in the northwest corner of Italy, where the borders of France and Switzerland meet. Although his mother was a pious Christian, his father was more concerned with worldly success. When a 15-year-old Anselm informed his parents that he hoped to enter the monastery, his father put the kibosh on the idea: “No son of mine will seclude himself behind those walls!”

Anselm decided to put some distance between himself and his father’s strictures by crossing the Alps, traveling across the French countryside, and landing in Normandy on the British Channel. He entered the abbey at Le Bec and strove to become a devoted member of the Benedictine order. By his mid-thirties, he’d advanced to lead the monastery as abbot. Like many such monasteries, Le Bec sponsored a school, and Anselm’s brilliant mind helped it become a center for learning that was the envy of religious pedagogy across Europe.

In 1066, William the Bastard and his armies crossed the channel to challenge other contenders for the British throne when King Edward the Confessor died without an heir. When he won the Battle of Hastings, Britain became French property. Anselm’s monastery at Le Bec benefitted when it was given land on either side of the channel. Overseeing those properties was the abbot’s purview, so Anselm traveled to Kent, where the people quickly came to adore him.

The Roman Catholic archbishop of Canterbury, whose domain included Le Bec’s British lands, died in 1089, and Anselm was chosen as his successor. Most of what we know about his work as archbishop is connected to his ongoing fight with the British monarchy over who should control the church of England. The king thought it was perfectly reasonable that he be allowed purview over the church’s revenues, its property, and the 11th century equivalent of its human resources department. The knock-down, drag-out battle was over investiture (the right to appoint people to church offices), which eventually the pope chimed in on. At the final buzzer, the score was King-0 and Church-1. Anselm was on the winning side.

As important as his role in the investiture controversy was, it’s his theology that Anselm is rightly famous for. Since Paul’s early forays into contending with Greek philosophy in places like his letter to the Colossians, and Augustine’s thinking that was steeped in a brand of Christianity shaped by Plato’s writings, the church had had to contend with the relationship between faith and reason. It was a chicken/egg question: which comes first?

Anselm put his substantial intellectual gifts into gear and gave us two major theological ideas: the satisfaction theory of the atonement and the ontological proof for the existence of God.

Anselm argued that faith and reason are partners. Theology and philosophy go hand in hand, but like the British kings and the church in the investiture battle, they each have a separate sphere of influence. Because they both come from God, they can’t contradict one another. Even so, Anselm said, our human reasoning abilities are tainted by sin and can’t avoid error. By itself, reason is too feeble to avoid error and can only be trusted when it’s illuminated by faith.

It was God’s revelation in Scripture, in the church’s teachings, and in Jesus himself that we encounter Truth that we’re called to believe. It’s only there that we can begin to understand anything in the world that we set our reasoning abilities to work on. His catchphrase was “Intelligo ut credam” or “I believe in order to understand.” In other words, we come to understand God not through our mind’s speculations but through faith. It’s faith, not the intellect, that is the door we pass through to access God. Given this revelation, Anselm put his substantial intellectual gifts into gear and gave us two major theological ideas: the satisfaction theory of the atonement and the ontological proof for the existence of God.

In Cur Deus homo? (Why Did God Become Human?), Anselm attempted to use logic to show why it was necessary for God to take on human flesh. It all revolved around the feudal legal system of medieval Europe. In this system of justice, if a person committed a crime against someone, that person was required to make satisfaction to the victim of the crime. The word we would use today would be restitution. But the fine and restitution the perpetrator had to pay in the feudal system didn’t depend on the nature of the crime. Its financial demands depended on the status of the victim. If you were a serf and victimized a woman or a fellow serf, the satisfaction required was fairly minor. But if your crime was against the nobility, then the law demanded an exorbitant penalty.

Anselm saw this as an analogy to what happened in the Fall. When Adam sinned, he carried the whole of subsequent humanity in his loins, which meant that both he and the rest of us human beings owed satisfaction to his (and our) victim. The problem was that in the Fall, sin was not perpetrated against another person; it was against almighty God. Having a king as our victim would have been bad enough, but having God as the victim of our sin required a proportional satisfaction. No human being could ever pay the boundless price against an infinite God. The only suitable penalty, then, was death.

But God, who is the immortal, invisible, God only wise, is also the God of grace and mercy. God wanted a return to the right relationship he had established in the garden, so satisfaction had to be paid. The only way to make it happen was by becoming a perfect blend: a God-Man. In Jesus of Nazareth, Emmanuel, God-With-Us, God offered up his own perfect, sinless life on behalf of every human being who had sprung bent and broken from Adam’s loins. The fine was paid. The satisfaction met. All because the Deus became the Homo in the title of Anselm’s work, whose atonement theory rendered moot all others to that point.

Perhaps more interesting is Anselm’s ontological proof of the existence of God. After his fellow monks suggested the topic and having wrestled with it night and day to the point of missing meals, he was certain he could find a way to prove God’s existence just from thinking about thinking. Ontology is thinking about being, so Anselm’s proof had to do with God’s Being. Here’s how the argument runs:

He’s properly regarded as one of the great doctors of the church, those teachers who helped Christianity plumb the depths of doctrine, Scripture, and a daily life of faith.

Your mind is able to conceive of a being than which nothing greater can be conceived. (Yeah, that’s an awkward sentence. But it’s Anselm. Just deal with it.) That being can’t merely exist in your thoughts; it has to be real as well. If it were just in your mind, there would have to be a greater being that existed in reality. That would contradict the original greatest being you conceived. That means this being has to be real both in your mind and in reality. And, brushing off the chalk dust from his hands, that, Anselm said, is God.

Anselm’s proof has led to gallons of ink being spilled on reams of paper through the century as other thinkers took issue with what he’d argued. Right or wrong, it’s the supreme example of how an entire era of Christian thinkers we call the Schoolmen or Scholastics attempted to understand Christian doctrine. Anselm tried to ground even the most complicated reasoning in faith. He died in 1109 and is buried at Canterbury. He’s properly regarded as one of the great doctors of the church, those teachers who helped Christianity plumb the depths of doctrine, Scripture, and a daily life of faith.