How do we know repentance and faith are essential for salvation?

Both Jesus and the Apostle Paul emphasized the importance of repentance and faith as fundamental aspects of salvation. In Mark 1:14-15, Jesus preached repentance and belief in the gospel, affirming that these are necessary responses to the approaching kingdom of God. Similarly, Paul, in Acts 20:21, proclaimed repentance towards God and faith in the Lord Jesus Christ as the core of his ministry. Thus, these elements are not optional but are central to the Christian faith, highlighting the need for a complete turnaround toward God through faith in Christ.