Romans 15:12-13 meaning

Paul continues quoting Old Testament Scriptures that demonstrate God's intention and promise to redeem the Gentiles (non-Jews). This shows that this was God's intent all along. Verse 12 starts with Again. This connects to verse 10, which says, "Again he says," then quotes biblical verses, but one is not written by Isaiah. This would indicate that the "he" of verse 10 either means "the prophet representing God's revealed word" or "he" refers to God who spoke through the prophets. Both amount to the same thing, as scripture asserts that God breathed the words of scripture but transmitted them through the agency of humans (2 Peter 1:20; 2 Timothy 3:16). 

Again connects with the previous section where Paul quoted Psalm 18:49, Deuteronomy 32:43, and Psalm 117:1 to demonstrate that the Old Testament predicted that Jesus would deliver the entire world (John 3:16). Now Paul quotes from Isaiah 11:1, 10:

Again Isaiah says,

"There shall come the root of Jesse,
And He who arises to rule over the Gentiles,
In Him shall the Gentiles hope" (v 12).

Jesse was the father of King David. God promised David that the Messiah would come from his family line and rule forever (2 Samuel 7:12-17). This of course refers to Jesus, the "Son of David" (Matthew 1:1). Jesus was the promised anointed one (Messiah) who will rule over Israel as well as the entire earth (Matthew 28:18; Hebrews 1:5,, 813; Revelation 3:21). 

This promises that Gentiles will have hope in this Jewish Messiah who is the root of Jesse. Paul could have in mind either Isaiah 11:1 or Isaiah 11:10, or both. The first speaks of a "shoot" that comes from the "root of Jesse." The "shoot" or branch refers to Jesus who is a human descendant of Jesse, the father of King David. In human form, Jesus descended from David through David's son Nathan (Luke 3:31). This genealogy from Luke is likely that of Jesus's mother Mary, who was made pregnant by the Holy Spirit (Matthew 1:20). 

This is significant because the kingly line descending through Solomon was cursed, saying that no more of that lineage would sit on the throne of David (Jeremiah 22:30). Jesus as the adopted son of Joseph had the legal right to reign (Matthew 1:6) but was not subject to the curse because His human descent was of God.

For further commentary on the root of Jesse possibly referring to the fulfillment of the prophecy that Jesus was to be a Nazarene, see commentary on Matthew 2:19-23. 

Paul's emphasis on Gentiles has particular relevance because Paul wrote this letter to the church in Rome, which is filled with Gentile believers (whose faith was spoken of throughout the world—Romans 1:8). For verse 12, Paul actually provides a reference, telling the believers in Rome he is quoting from Isaiah. He doesn't add the chapter and verse because at that point in history the numbers and chapters had not been added. Chapter and verse breaks are not original, they were added later to facilitate reference and study. 

Paul then offers a blessing and prayer of sorts, Now may the God of hope fill you with all joy and peace in believing, so that you will abound in hope by the power of the Holy Spirit (v 13). The letter is coming to a close, and Paul offers further encouragement that his readers continue to place their hope in God. He uses Isaiah's prophecy to prove Christ's acceptance of the Gentiles; Christ is the root of Jesse, He has inherited the earth (Philippians 2:8-11), and the Gentiles now praise Him (Romans 1:8) and have hope in Him. Christ has conquered, and we who believe in Him experience God's mercy and grace.

The phrase joy and peace in believing demonstrates that Paul's emphasis is to walk in faith. Both joy and peace are byproducts of an ongoing belief, walking in faith that God's ways are for our best. As Paul already emphasized, it requires a renewed mind, a change of perspective, to believe that conducting our lives as living sacrifices is actually in our true self-interest (Romans 12:1-2). This then is a bookend to the theme verse, where Paul asserted that actual righteousness comes through a walk of faith, believing God's ways are for our best, rather than a walk of pride (Romans 1:16-17). 

The power to walk in such faith (in believing) comes by the power of the Holy Spirit. It is in the power of Jesus's resurrection that we can put to death the flesh, which is sin dwelling within us (Romans 7:17). The Holy Spirit can give us new eyes to see that walking in our own ways of pride and flesh actually lead to death (Romans 6:23; Galatians 6:8). 

Throughout this chapter, Paul has encouraged the believers that they can have hope. Paul has said that God gives us hope through perseverance and Scripture (Romans 15:4), Christ (v 12), and the Holy Spirit (v 13). We have joy and peace when we anticipate and believe that the promises of God will be fulfilled. When we have faith in God and follow His ways, we are granted hope by the power of the Holy Spirit that the rewards God promises will be fulfilled.

Much of Paul's purpose in writing this letter was to clarify that living the way God designed us to live comes through faith, not law, sin, or flesh. Paul has contended with competing Jewish "authorities" who slandered Paul's gospel (Romans 3:8). He soundly defeated this slander, showing that righteousness (living as God designed) is accomplished by faith. Living by faith looks like following the Holy Spirit, the Helper (Romans 8:13-17).

Paul asserts to his audience that he hopes now, at the end of this letter, they would be at peace, and rest in hope in the Spirit, rather than worry about following the Law. Paul has emphasized faith in God, rather than rule-following, and this is accomplished through the Holy Spirit, who dwells inside each believer. In verse 13, it is also by the power of the Holy Spirit that we can be full of hope. Hope, joy, and peace are given to us by God and the Spirit, by living out our faith.