Romans 15:7-13 (NLT)
7 Therefore, accept each other just as Christ has accepted you so that God will be given glory. 8 Remember that Christ came as a servant to the Jews to show that God is true to the promises he made to their ancestors. 9 He also came so that the Gentiles might give glory to God for his mercies to them. That is what the psalmist meant when he wrote: “For this, I will praise you among the Gentiles; I will sing praises to your name.” 10 And in another place it is written, “Rejoice with his people, you Gentiles.” 11 And yet again, “Praise the Lord, all you Gentiles. Praise him, all you people of the earth.” 12 And in another place Isaiah said, “The heir to David’s throne will come, and he will rule over the Gentiles. They will place their hope on him.” 13 I pray that God, the source of hope, will fill you completely with joy and peace because you trust in him. Then you will overflow with confident hope through the power of the Holy Spirit.

Paul in this part of Romans is winding up his epic work. His theme throughout has been the Gospel, the good news of Jesus Christ (see Romans 1:1-5). Paul begins as he finishes describing how God will bring all nations together in Jesus Christ and that through Him they can know of love, hope, joy, peace.

When we talk about joy many people think happiness. That’s not what Paul means here (doesn’t exclude happiness, but it is not limited by it). Joy doesn’t mean feeling good all the time.

Joy is a settled confidence or assurance that God is in control of every detail of life, leading to a contentment in the soul that is expressed in thanksgiving and praise.