Common noun, genitive, masculine, singular. Here it qualifies the preceding noun, thelematos; it is His will that Paul should be an apostle. Paul did not choose to be an apostle; nor can he (or anyone else). It is an office by special invitation and appointment. This is the basis on which Paul, therefore, speaks. His authority is not his own but derives from an altogether higher source. The Corinthians may argue and question it but, for Paul, it is a non-negotiable. He has to speak what he does because he is under order and commission.
Open Alberith Greek Wordbook on theos
©ALBERITH