How do we know God will save lost souls?

We know that God will save lost souls based on His sovereign will and the complete sufficiency of Christ’s redemptive work. In Romans 9:18, Paul highlights God's absolute authority: 'Therefore hath he mercy on whom he will have mercy, and whom he will he hardens.' This illustrates that salvation is ultimately in God's hands, according to His purpose. Furthermore, the ministry of reconciliation through preaching is God's chosen means for calling His elect out of darkness into His marvelous light. The assurance lies in the promise that God will notify His chosen ones through the Word proclaimed. Thus, while we may not know who will be saved, we are confident that God will fulfill His promise to gather His people, as expressed in the comforting truth of the gospel.