How do we know the doctrine of two natures in believers is true?

The reality of the two natures within believers is supported by Scripture, particularly in Romans 7:18-25. Here, Paul identifies the ongoing struggle between the flesh—representing the old nature—and the spirit, which reflects the new nature birthed in regeneration. Every believer experiences this internal conflict, recognizing the presence of sin and the longing to obey God's law. This struggle is a testament to the transformative work of grace and the indwelling of the Holy Spirit in the believer's life.