How do we know that Christians still struggle with sin?

In Romans 7:14-25, Paul clearly delineates his own experience of wrestling with sin even after his conversion. He states, 'I am carnal, sold under sin,' which underscores that despite being saved, he still faces challenges with his sinful nature. This passage shows that the presence of sin remains in the life of a Christian, leading to an inner conflict between the desires of the flesh and the work of the Holy Spirit. Such struggles serve to confirm the reality of a believer's faith, as true believers seek to fight against sin rather than succumb to it. Moreover, the ongoing battle illustrates the need for continual reliance on Christ’s righteousness and the grace of God.