2Th 1:8 In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ:
2Th 1:9 Who shall be punished with everlasting destruction from the presence of the Lord, and from the glory of his power
"Obey not THE GOSPEL"....
What is the gospel? What is the "good news" and how do we "obey" it?
From what Jesus has taught me in His word, THE GOSPEL is the good news that He paid the price for my sin, and I am to trust in Him and His finished work. I am supposed to REST IN JESUS, but without His help in this, it is something I cannot do...and I confess that I cannot do it, and REST in the fact that Jesus can, and does, and already did everything to secure that for me, and that is GOOD NEWS (gospel) indeed!
EDITED TO ADD
Gregg at Gospel Driven Disciples has the word GOSPEL for his A to Z challenge word for today. He has some excellent info on that excellent word here