"Therefore, having been justified (or made righteous) by faith (or faithfulness) we have peace with God through our Lord Jesus Christ" With this sentence, Paul sums up the point he was making in the first unit of his letter (chapters 1-4) and begins the second unit of this epistle (chapters 5-8). In the first unit of the letter, Paul argued that Jew and Gentile alike were in need of being made righteous and that God had done this apart from the Law in Jesus Christ. Paul also began to argue that God was righteous for having done this; a theme which he will pick up again in Romans 9-11. In the letter's second unit, Paul will go into more detail about how exactly God has made us righteous through Jesus Christ and he begins by speaking of the remarkable love of God.
In the opening verses of this section, Paul says that "we exult in the hope of the glory of God". This is a somewhat ambiguous phrase. What exactly does it mean to exult in the hope of the glory of God? The idea of hope points toward a future event since we don't hope for things that are already present. Therefore, it is likely that Paul is referring to the final day of judgment when God will reveal God's glory to all of creation. Why would Paul's audience exult in this? Precisely because of what Paul has just said, they have peace with God. Christians can actually look forward to the final revealing of God's glory since it will be the day when their salvation will be made complete. God's judgment will not mean punishment and wrath for those whom God has already made righteous. It will mean that God's righteous judgment will bring righteousness to the rest of creation as well.
However, Paul recognizes that until that final revelation of God's glory, there will be suffering and tribulation which, ironically, Christians can exult or rejoice in as well. Paul says this is because suffering procudes character and character produces hope so that when God is involved in the process of suffering it becomes a kind of upward spiral where hope just produces more hope. But Paul wishes to make clear that this hope is not a fool's gold or a mirage which only vanishes when we really need it. This hope does not dissapoint us because it is grounded in the audience's experience of God's love.
The recipients of this letter have experienced the love of God primiarily in two ways. The first one, which Paul mentions in v.5, is God's love being poured into their hearts through the gift of the Holy Spirit. This is the more subjective experience of God's love which the saints in Rome would have experienced when they first became Christ-followers. The book of Acts attests repeatedly that there was a palpable reception of God's Spirit by believers when they were first baptized. Paul also uses the presence of the Spirit as a mark of truly receiving the gospel in his letter to the Galatians (3:2-3). The Roman church can persevere in trials because there hope is founded in the very real experience that they had when the Holy Spirit was given to them and they began to feel the love of God transform them.
God's love has also been revealed to Paul's audience through a less personal, more objective means; the faithfulness of Jesus Christ. Pauls says that while we were still helpless, godless, sinners and enemies of God Christ died for us and God's love is demonstrated in that fact. After all, who chooses to die for their enemies? No one! People usually will not even give up their life for a righteous person or someone that they respect or to whom they are indebted. The incredible length and depth of God's love is demonstrated by the fact that God himself, through the person of Jesus Christ, has taken on death for those who were at war with God. Paul goes on to say that is why our hope in God is so sure. If God has accomplished the incredible task of making peace with his enemies, then clearly God will accomplish the much easier task of saving those with whom he made this peace.
The theological implications of this passage are vast. Paul continues to show how God's righteousness is revealed in the gospel, now in terms of love. In doing so, he is also laying down an implicit ethic of love for his congregation; an ethic of love that is so strong that it calls us to sacrifice for the sake of our enemies because that is what God did for us. Furthermore, Christians can make that kind of sacrifice because of the hope they have found in God's love.