What does the Bible say about confidence in oneself?

In Philippians 3:3, Paul instructs believers to worship God in the Spirit and rejoice in Christ Jesus, commanding them to have no confidence in the flesh. This highlights that any self-assuredness based on human ability or achievements is ultimately worthless in the sight of God. The Apostle Paul offers a strong testimony of his own qualifications and achievements, stating that even those are deemed as loss compared to knowing Christ. True confidence for a believer must come from reliance on Christ's completed work rather than on self-effort or accomplishments.