How do we know that the doctrine of holiness is true?

Believers are called to holiness in 1 Peter 1:15-16, which states, 'But as he which hath called you is holy, so be ye holy in all manner of conversation; because it is written, Be ye holy; for I am holy.' This command reflects not only God's character but also the transformative work of Christ in believers. Being made new creations in Christ means that they now possess a nature that desires to live righteously. Though they will struggle with sin, the command to be holy points to the ongoing work of God in sanctifying His people, making it both a reality and an expectation for those who are His.