His new name, the narrator points out, will "live in that country as long as the (scarce more) glorious one of the great Roman." The narrator then continues saying that Oroonoko has just as much courage anyway.
I felt that this name exchange was important because readers gain insight into how revered of a man Oroonoko is from an insiders view of the story through Tefrey, as well as gain the story teller's personal opinion of how great a man this is - only slightly less glorious than Julius Caesar, himself.
The thought crossed my mind that perhaps Oroonoko's new name was foreshadowing to his leading an army of slaves, then being killed by those closest to him. I was halfway right. He did lead an army of slaves and although they were on the same level they bowed and kissed his feet; but instead of getting killed by those closest to him, he ended up killing the one he loved most-Imoinda. Although he killed her with the best intentions, I believe that this act was a far greater punishment than having extremities cut off one by one.
FUN FACT WEBSITES!! :
Meanings behind latin prefixes (try Oro and Cae!)
Baby name meanings (why you shouldn't name your kid a variant of Caesar)