Arabic writing
The visual beauty of the Arabic written language is a symbol in this book for the lovely culture that Omar Ibn Said comes from, and it is a symbol for his attachment to that beautiful culture. Arabic writing is also closely associated to the Quran in the book, so the writing symbolizes his primary attachment to his Middle Eastern education and point of view. This is contrasted with English and Christianity.
Omar's symbolic Christianity
When Omar is presented with Christianity, he decides that because of the symbolism of Jesus's teachings, he would consider himself a Christian. The symbolism of Christianity, of oneness with God, and of love between God and humans as the love of a father (he specifically mentions Jesus's famous prayer in the Sermon on the Mount) resonate with Said, but that "conversion" is an affinity toward Christian symbols. He never abandons his original faith. He doesn't have to it seems.
Conversion as a culture statement
Having converted to Christianity makes Omar Ibn Said a celebrity. Not only that, it permits him access to a better life than he would otherwise have had. So one might conclude from this that Christianity is a kind of pass that he gets to use to have a better life. It also symbolizes that Islam left him open-minded, because one would not expect any of his community to return the favor and see the beauty and value of his person views of the Quran, but he does that for them.
Capture as a sign of fate
Omar is a slave, so his capture is a symbol for fate, because his station in life radically changes, and he is forced to adjust and adapt to a new life where he is mistreated, where people dehumanize him. His story is similar to the story of Joseph in the Abrahamic religions, because Joseph is sold into slavery and also goes to a new nation where he has to make a way for himself with no help.
The abusive infidel
Omar says that his first owner is obviously an infidel ('fid-' means faithful in Latin, so infidel means "faithless"). He says this because the man claimed to be Christian, but he violated every single teaching of Jesus Christ without fear of repercussions. Omar views him as a symbol for hypocrisy, because he uses the religion to feel better about himself, but he still behaves hatefully and abusively.
