[Ali Imran]

Galatians 1:8

But even if we or an angel from heaven should preach to you a gospel contrary to the one we preached to you, let him be accursed. 8 Let God's curse fall on anyone, including us or even an angel from heaven, who preaches a different kind of Good News than the one we preached to you.

Yes, Paul wrote that. Why did he say that? 

That is the question you should ask.