“Obeying the gospel”

I was reading through the Q & A and came across the following as a portion of your answer to someone.... “He [the Lord Jesus] will punish those who do not know God and do not obey the gospel of our Lord Jesus." Since the gospel is all about what God has done to save us and it is not about anything we do, what does it mean to "obey the gospel"? Thank you.

The apostle Paul’s inspired words from 2 Thessalonians 1:8 can certainly strike us as sounding strange. His words describe people who reject the gospel of Jesus Christ. 1 Peter 4:17 contains the same message.

In Acts 26:19 the apostle used similar language when he spoke of God giving him faith to believe the gospel: “I was not disobedient to the vision from heaven.”