This letter to the Romans is all about the 'gospel': the word simply means 'good news'. Paul is not describing an idea he has invented, because this good news comes from God (Romans 1:1).
When God calls people to repentance and faith, He also calls them to serve Him. In Paul's day, slaves were legally 'bound' to their masters; and he used that word to describe his service to God.
Paul was totally committed to the gospel. The good news about salvation through Jesus was the apostle's passion. He knew the message was powerful to bring people to faith: Jews and Gentiles alike.
Because God is the source of all wisdom, rejecting Him is the ultimate foolishness. We can reject Him passively as well as by outwardly hostile aggression.