“But even if we, OR AN ANGEL FROM HEAVEN,
preach ANY OTHER gospel to you
than what we have preached to you,
let him be accursed.
As we have said before, so now I say again,
if anyone preaches any other gospel to you
than what you have received,
let him be ACCURSED.”
Galatians 1:8-9

Tough words. But crucial. He states it twice, thereby calling specific attention to it.

Why is there a curse on anyone preaching a Gospel different from the one the Apostles gave us?

Because God has provided only one atonement for us, his Son Jesus Christ who was tortured and crucified in our place, paying such a heavy price for our salvation. That atonement is the ONLY way that one can be saved.

Satan hates the Gospel, and he constantly tries to turn the eyes of mankind away from it. He doesn’t care what you believe as long as it isn’t the truth. He has many counterfeits, and he works diligently at bringing people into the many false religions he has established.

There are terrible consequences to that, so much so that the Scriptures pronounce a double curse upon anyone who brings a “gospel” other than the true one. It mentions specifically those brought by a supposed angel, for example the “angel” Moroni of the Mormons, or the “angel” who supposedly gave Mohammed his perverted message resulting in Islam. These are actually under the CURSE of almighty God.

“Nor is there salvation in any other,
for there is no other name under heaven
given among men -by which we must be saved.”
Acts 4:12

“I am the way, the truth, and the life.
NO ONE one comes to the Father EXCEPT through me.”
John 14:6

For the Son of God to pay such a terrible price, there must be something terrible to avoid.

More:
Who Is Jesus Christ?