When God calls people to repentance and faith, He also calls them to serve Him (Ephesians 4:1).  In Paul's day, slaves were legally 'bound' to their masters as ‘bond-slaves’; and he used that word (translated here as ‘debtor’) to describe his service to God in preaching the gospel to Gentiles as well as Jews.  

Paul was not grudgingly obedient to God’s call.  His love for his Saviour gave him the overwhelming desire to serve Him for ever (Deuteronomy 15:12-17), by taking the gospel to every kind of people irrespective of religious background or lifestyle.  

Although the apostle had a special commission to preach the gospel to Gentiles, he never limited his ministry so that Jews were excluded (Acts 9:15).  Although Paul's background was academic learning in a university, he knew that the gospel was for poor and illiterate people as well as for the educated.  Rome had them all!  Every sort of person from all cultures and religions lived there or came to trade.  It was an ideal place to preach the gospel of Jesus that is for everybody.

True disciples of Jesus Christ know that they are under an obligation to serve their Saviour.  'Following Jesus' is not a codeword for joining a club of nice people, nor is salvation just a certificate to enter heaven.  Although we all come from a unique background, the Lord will call us to serve Him in any way He pleases.  Those who understand that the blood of Christ has 'bound' them in service to Jesus will be willing to do whatever He says and go wherever He sends.  That does not only apply to missionaries - it is normal Christian discipleship. Even today, the Lord wants to use you; are you willing? As you do your usual work, try to see every task and encounter as an opportunity to serve your Saviour (Colossians 3:23-24), and let Him lead you wherever He chooses.