Why does Paul defend his apostleship in 1 Corinthians 9?
Paul defends his apostleship because it was continually questioned, and he needed to affirm his authority and freedom in Christ. He asks whether he is not an apostle, not free, and whether he has not seen Jesus Christ our Lord, establishing his apostolic standing and liberty.
Les explains that the Apostle Paul is always having to defend his apostleship, and 1 Corinthians 9 is another instance. Les notes that Paul opens with the rhetorical questions, "Am I not an apostle? Am I not free? Have I not seen Jesus Christ our Lord?" This defense arises in the context of Christian liberty: believers have legitimate freedom under grace, but they should voluntarily limit that freedom if exercising it would cause offense to others, especially unbelievers, so as not to hinder their becoming believers. Paul's defense of his apostleship thus fits his broader concern for others' consciences.
Am I not an apostle? am I not free? have I not seen Jesus Christ our Lord? are not ye my work in the Lord?