Islam and community care
Lily's opinions of religion are formed by her experience as a literal orphan, so she understands an aspect of Islam that other people understand through lip-service. She knows what it's really like to be on the wrong end of the social hierarchy, and she knows what it is like to be taken from home, to lose one's parents abroad, and when she grows up, she gives her life to social work. Her Muslim faith is her impetus to use her life to improve the lives of those in her community.
Judgment and prejudice
Aziz and Lily have more in common than their consonant patterns of their names; they also are inverse opposites: Lily is too white to fit into her community, and Aziz is too dark. This shows that prejudice is unfounded and brutal, and that the sufferers of social rejection can find solace in their own community. Aziz and Lily are a family, and we know that because when they are separated, Lily is true to him, a sign of her sureness in their love.
Social order and chaos
Lily has to evacuate her home in Ethiopia when the revolution begins there. The violence is a sign that the community is striving for a new order, but the chaos of the transition is so dangerous that she must leave to go back to London, even though her life has been set in a different part of the world for most of her waking life. When she gets to London, there is order, but only because people assume she is like them. So she introduces a plea for new order by loudly declaring her Muslim faith in a nation where that is an unusual behavior at best.