Brotherly Appeal (Philemon 8-16)

Paul has the authority of an apostle.  This means that Paul can give a command and it is as if Christ gives the command.  Paul makes a big deal not to appeal to his apostolic authority when he exhorts Philemon.  Why does Paul use so many words rather than simply write, “I command you to forgive your brother who ran away!”  Why does Paul try so hard not to constrain Philemon through forceful words?