Xury the slave boy is only a minor character in Robinson Crusoe, but his brief appearance tells us an awful lot about what kind of person Crusoe is at this stage of his journey.
Crusoe has been enslaved, which one might think would make him detest this abominable institution for all it was worth. But, as subsequent events will show, that's not the case. Crusoe may think it contemptible for a white Christian man such as himself to be enslaved, but not for non-white pagans.
In any case, Crusoe manages to escape his confinement, along with Xury and another slave. Crusoe forces the other slave to swim to shore, but allows Xury to remain aboard his boat. In effect, Crusoe is showing Xury that he trusts him.
In due course, that trust will be repaid, but Crusoe will go on to betray Xury. When the Portuguese captain picks them up, Crusoe sells Xury to him, an indication that, despite his beneficent treatment of the boy never saw him as anything more than a slave, a piece of property to be bought and sold.
Though Crusoe has been able to break free from his bondage, he hasn't yet emancipated his mind from the shackles of colonialism and white supremacy.