The tone and content of this letter show that Paul did not seek to win people's approval. The Judaizers likely criticized Paul for trying to please people by focusing only on faith and grace, not including the law, which they saw as the whole message.
Being Christ’s servant means staying true to Christ, no matter how others react (see Acts 5:29; Ephesians 6:5–6; 1 Thessalonians 2:3–6).