How do we know that God saves sinners through the gospel?

God's method of saving sinners is through the foolishness of preaching, as Paul underscores in 1 Corinthians 1:21. The gospel is the power of God for salvation, and it is through this proclamation that the Holy Spirit works to bring the elect to faith. Scriptures consistently assert that those chosen by God will ultimately hear the gospel, as shown in classic examples like the Ethiopian eunuch. God has determined before the foundation of the world to save a chosen people, and the means He has ordained for this is the preaching of the gospel. Thus, true gospel preaching is essential for the salvation of His elect.