What does the Bible say about why God allows sin to remain in us?

According to Romans 7:11-20, God permits sin to persist in our lives to continually remind us that our salvation is entirely by grace. If God took away our sin upon salvation, we might become overly confident in our own righteousness. The pervasive presence of sin in our lives serves as a constant reminder of our need for grace and the sufficiency of Christ's atoning work. Paul highlights this struggle, noting that even he, as a mature believer, grappled with sin, leading to a deeper dependence on God’s grace.