What a wonderful final paragraph for Paul to write to the believers in Rome.  It is a summary of the gospel through which the church came into being.  Of course, God knew about sin even before it entered the world, and He laid down a plan to rescue His people from its grip (Ephesians 1:4-10).  He chose that salvation would come through Jesus; but His people needed to be prepared, and so the Old Testament narrative is studded with hints of Christ's ministry.  But God’s people did not understand (2 Corinthians 3:13-15).

But the mystery of the gospel was hidden until Pentecost.  Even during the ministry of Jesus the disciples did not really understand (John 12:16).  Even the resurrection was a puzzle to them (John 20:9).  But when the Holy Spirit came at Pentecost, the apostles could see the whole plan of salvation and understood God's revelation in the Old Testament scriptures (Acts 2:29-39).  

The apostles' task was simply to proclaim Jesus Christ as God's answer to sin and rebellion in the world; and to encourage people to believe in Jesus and do what He commanded.  It was the apostles’ doctrine (Acts 2:42) which built, sustained and protected the Early Church.  There is no other sound teaching; if they were to substitute another gospel, they would not hope in Christ (Galatians 1:6-9).  If they did not hold firmly to the apostle’s teaching, there is no eternal security (1 Corinthians 15:2)

This gospel still applies to every group of people in the world.  Therefore, we can safely take Paul's letter and use it to explain the gospel to anybody.  It is only through God's wisdom that salvation's plan was conceived and executed. Although it is certainly true that all who believe have great blessings, and are no longer under the wrathful condemnation of God, ultimately the purpose of the gospel is that God should be glorified for ever - because of His amazing wise kindness in saving people through the sacrificial blood of Jesus Christ.  The church is the evidence that Jesus saves!  And God gets the glory.