Why is the gospel of grace considered heresy by some?

In the sermon, it is noted that when Paul was queried about the sect he preached, which was the gospel of God's grace, the hearers called it heresy. This reflects a broader contemporary struggle where people are inclined to adhere to a gospel molded by human works, rather than accepting the divine revelation of grace. Paul clarifies in Galatians 1:11-12 that this gospel is not from men but delivered by revelation from Jesus Christ. Thus, those who adhere to a works-based salvation naturally misconstrue the grace-centered gospel as heretical because it undermines human pride and autonomy.