How do we know that everyone who believes in Christ is a saint?

The assurance that all who are in Christ are deemed saints stems from the regenerative work of the Holy Spirit. Paul articulates this in 2 Corinthians 5:17, proclaiming that anyone in Christ is a new creature, indicating a fundamental change in identity. This transformation signifies that all true believers, regardless of their past, are now recognized as saints, set apart for God's purposes and called to follow Him wholeheartedly. Hence, the term 'saint' encompasses everyone who has sincerely placed their faith in Jesus Christ.