Paul apparently is alluding to Jewish traditions outside the Hebrew scriptures that tell of Satan disguising himself as a shining angel when he deceived Eve in the Garden of Eden. On Satan see comments on 2.11.

And no wonder that these false apostles behave in deceptive ways and disguise themselves to be what they are not; even Satan, who is their master (verse 15), behaved in a similar manner. Some languages may require a full verb phrase at this point: “It is no surprise that they do this!” or “we should not be astonished that this happens.”

Disguises himself: or, as in the previous verse, “tries to make himself look like…” or “tricks people into thinking he is….”

An angel of light: the relationship between the words angel and of light may be that the angel (or, messenger) brings light. But more likely Paul’s thought reflects Jewish traditions in which Satan appears in the form of a shining angel in order to deceive people. The words of light function as an adjective, that is, “a shining angel” (An American Translation). Most translations keep the form of the Greek, angel of light. Some omit the words of light (Die Bibel im heutigen Deutsch, Parola Del Signore: La Bibbia in Lingua Corrente), since angels by nature shine with light. Translators should translate the words of light. An American Translation is a good model, since it expresses clearly in English the Semitic influence on the Greek grammar here.

Quoted with permission from Omanson, Roger L. and Ellingworth, Paul. A Handbook on Paul’s Second Letter to the Corinthians. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .