Why does the Gospel offend people?

The offense of the Gospel emerges from its radical declaration that salvation is by Christ alone, entirely disconnected from any human merit. As explained by Paul in 1 Corinthians 1:23, preaching Christ crucified becomes a stumbling block to both Jews and Gentiles. The natural man is inclined to seek validation through his works and desires to contribute to his salvation; however, the Gospel declares that all who are saved are done so through Christ's work alone. This affront to human pride and self-sufficiency is what makes the way of salvation offensive to the unregenerate heart. It challenges the intrinsic idea of earning favor with God, presenting instead a grace that is wholly unmerited.