One True Gospel

¹¹ I want you to know, brothers and sisters, that the gospel I preached is not of human origin. ¹² I did not receive it from any man, nor was I taught it; rather, I received it by revelation from Jesus Christ. (Gal. 1:11-12)

Paul makes big bold statements all throughout the book of Galatians, and in Chapter 1 makes no attempt to shy away from how angry and disappointed he is with the people of Galatia. They had rejected the gospel he taught them for another one, which did not have any real substance to it.

Why was it so easy for the Galatians to forget the true gospel? Why is it so easy for us to do the same today? And in a world with so many shades of grey, what does it actually look like to believe the teachings of the gospel of grace that was revealed to Paul (and now to us) directly by Jesus Christ?