I had an Arabic friend's dad read this for me, and tell me a bit about it.

Backstory: my friends dad is from Egypt. He is a native Arabic speaker, who knows English and teaches religious studies at a local University. He immigrated to the US with his wife when he was 34.

He says that it's a prayer meant to guide spirits to their final resting place. The prayer is from those who have unpaid dues/ other unfinished business with the person who has passed. It's like, a forgiveness prayer of sorts, but its also a prayer to ask for forgiveness.

He says he's not sure of the angel thing, but he believes it to be a Jinn. It's an Arabic spirit of sorts, made from bone and marrow, like humans, and then changed by the world. He believes this jinn to be an illustration of a families protector of sorts. Kind of like a guardian angel, but the Arabic version of it. He also said that jinn aren't often illustrated with wings, but that's it's not unheard of.

He thinks that this is an offering of peace from someone who once knew your friends grandfather. The image of the jinn is an offering of his families guardian angel, a token of spirituality. Whoever left this believes that they owe your friends grandfather something, and they're paying with their families spiritual guardian, but it could also be that your friends grandfather owes the person who left this something, and they're extending forgiveness and offering their jinn in support.

Also, someone earlier said that jinn were creatures with hooves that lived underground, but in Arabic culture they are not.