How do we know the gospel is essential for salvation?

The gospel consists of the good news of Jesus Christ's death and resurrection, which provides the only means for sinners to be reconciled to God. In Romans 1:16, Paul indicates that the gospel is the power of God for salvation to everyone who believes, affirming its centrality in the redemptive process. Moreover, in Ephesians 2:8-9, we see that salvation is by grace through faith and not by works, highlighting that it is through belief in the gospel that one receives the righteousness of Christ. This truth emphasizes the necessity of preaching the gospel, as it is the means by which sinners are drawn to repentance and faith, leading to salvation.