This book leaves me convinced of one thing: St. Catherine of Siena was one of the greatest saints of all time.

I have been familiar with parts of Catherine's story for a good deal of my life; I remembered her childhood playing at prayer, her retreat to a room of her parents' house as a young person, some of her mystical experiences, her leaving of the room to serve the poor and sick, putting up with very nasty treatment from some of them out of love for Christ. I also knew that it was because of her mission that the Popes returned from Avignon to Rome. But what surprised me as I read this was just how much of a political force Catherine was in the Italy and Europe of her day.

She wrote -- dictated -- a lot of letters, to the most important people of her time, as well as to her personal friends in lower strata of society. She wrote invective, she wrote powerful persuasion, she called everyone to seek the glory of God and the salvation of souls. In her life, we see a direct and powerful connection between the life of the soul and the life of the city, between faith and politics. We see, Undset points out, common sense and great intelligence co-existing with extraordinary mystical gifts, a sacrifice of self for love of Christ and souls. We also see how fiercely God Himself cares about the affairs of human beings in the temporal world.

This is an outstandingly good saint's biography. Both secular and religious biographers of saints often bring severe limitations to their material. Undset surely has her limitations too. But she was already a great novelist, with years of immersion in the Medieval world behind her, when she began her version of Catherine's life. That life was many-dimensioned. Not only does this biography not exhaust it but it partakes somewhat in the quality of its subject, in not being possible to exhaust with a single reading.

I was particularly intrigued by how some of Catherine's revelations anticipated the revelation of Divine Mercy and especially the devotion to the Precious Blood that are spreading through the Church of today. I would like to trace those themes someday, in the writings of Catherine herself.

In a tangent about St. Birgitta of Sweden, another saint who urged the Popes to return to Rome (before Catherine's success), Undset writes: "Grace does not alter our natures, it perfects them." A clue to Catherine's nature is found in an utterance made in one of her ecstasies: "In Your nature, Eternal Divinity, I have learned to know my own nature . . . My nature is fire."

To read this book is to catch a little of that fire. ( )