These four rhetorical questions expect a positive answer. The first question, following his discussion in 8:1–13, asserts Paul's freedom from Jewish ritual obligations. However, he later emphasizes (see 9:19–23) that he willingly follows Jewish practices to win them to Christ. The other three questions assert Paul's apostolic authority, which some in Corinth questioned.
For you are the seal: For skeptics, Paul's apostolic calling was confirmed by his encounter with Jesus on the road to Damascus (see 15:8; Acts 9:3–6, 17). Also, the Corinthians, who came to faith through Paul's evangelism (see Acts 18:1–11), were proof of his status as an apostle.