Blanquerna, was written in the 1200s by Ramon Llull, who was a missionary, philosopher, and Crusade propagandist. He wanted to use philosophy to teach Muslims the truth about Jesus, so he learned Arabic and traveled to North Africa, where he was unsuccessful at some personal risk. He was influenced by Muslim culture to some extent, incorporating Sufi elements in The Book of the Lover and the Beloved. I don't think he should be viewed as a multiculturalist for that. I think he would have viewed the Sufi element as something belonging to Christ originally. (That's a speculation based on the fact that his writing is heavily Christian, he wanted to convert Muslims, and he was in favor of the Crusades. It was more or less the view of Simone Weil about elements she liked in non-Christian religions). But for his time, he was more liberal (or, more Christian in the "My kingdom is not of this world" sense) by wanting to persuade Muslims using philosophy, something which most people in his day didn't think worth trying.
I read Blanquerna over a period of about four years. I was drawn to it because it contains The Book of the Lover and the Beloved, which has short sayings, one for each day of the year. (I read through them that way, which accounts for one of the four years.) The overall book Blanquerna is a story of a young man who wants to be a hermit, but first has to have a career in the church. He ends up being pope. The Book of the Lover and the Beloved I can recommend to most people who would be reading this review (it's in the public domain and can be found online, separate from Blanquerna), but I struggled to get through the rest of the book. The style can be dry and slow. Llull was a philosopher and uses the events of the plot to illustrate ideas and has characters be his mouthpiece. The style and ideas probably seemed more legible to his medieval contemporaries, but were foreign to me. I think it's valuable to spend some time in foreign thought-worlds, foreign writing-style-worlds, and when I wasn't stunned by the process of reading, I found ideas I'm not sure I could find in modern books. One from near the end (Ch. XIII, paragraph 7, of the Art of Contemplation, one of the books involved in the overall story) is, in my words, "In your struggle against sinful habits you experience faith, hope, and love, virtues which help you deal with those habits, so pray for those virtues and the grace to forget the habits." Llull was interested in holiness, not as much a contemporary concern. A point a person could add to his is that acquaintance with God and the virtues is what God really wants for us, not some bare sinlessness. I don't think that means that sinlessness is not essential (I would guess that Llull wouldn't have supported that view), but that there's a positive content to holiness as well as a negative, pruning motion. Another idea that I like I've already posted, his illustration of a man and a woman discussing why he loves her.