Why is the gospel considered offensive to some people?

The gospel's message, especially the concept of salvation being a free gift, contradicts the natural inclination towards self-reliance and works-based righteousness. In John 16, Christ prepares His disciples for the inevitable opposition they will face from the world, which often responds with hostility to the message of grace. As expressed in 1 Corinthians 1:23, the message of the cross is foolishness to those who are perishing. This offense arises because the gospel demands recognition of our inability to save ourselves and reliance solely on Christ's righteousness, which many find difficult to accept.