How do we know that faith is the effect of salvation?

In the sovereign grace perspective, faith is understood as the effect of salvation rather than its cause. Paul presents this clearly in Romans 5:1, where he states that believers are justified by faith, indicating that this faith is a response to God's justifying grace. God chooses His people for salvation and sends the Holy Spirit to regenerate their hearts, enabling them to respond in faith. Thus, every believer who is justified will invariably come to faith, confirming that salvation originates from God, not from human effort.