What does the Bible say about the two natures in believers?

In Romans 7, Paul describes the internal conflict that every believer experiences due to the presence of two natures. One nature, referred to as the 'flesh,' is inherently sinful and serves the law of sin. The other nature, the 'spirit,' is oriented towards God and seeks to do good. This duality illustrates the ongoing struggle within Christians, who, despite their spiritual desires, are continually hindered by their sinful flesh. While the flesh remains unchanged and corrupt, the work of grace empowers believers to walk according to the Spirit.