Romans 15:1-13 - Loving the family
Paul wants Christians to learn to be less selfish and more selfless. Less like their old sinful selves and more like the people God made them to be - more like Jesus.
This means Christians should be increasingly patient with each others' weaknesses and failures. Jesus has made them family and a loving family is one that helps people in it to grow. This happens when each member of the family is thinking about what the others need before they think about their own needs. They give more than they take. They serve others instead of expecting others to serve them. In this way, Christians are copying Jesus, who despite being God(!), put the needs of others first, gave more than he took and served others instead of expecting others to serve him.
Paul says the Bible teaches endurance and provides encouragement. The God who wrote it gave endurance and encouragement to Jesus and offers it to those who trust and follow Jesus so that they might worship and please him as Jesus did. This means they don't love each other in their own strength but they trust God to give them himself and everything they need through his word (the Bible) to love each other well.
If Christians could endure and encourage one another more, there would be more unity. This is Paul's main point. One of the signs that someone is really trusting and following Jesus is that they endure and encourage other Christians regardless of their background or where they come from because God's plan from the beginning has been to have a family of all kinds of people from all nations.
Christians have often struggled to love each other and today, if we're Christians, we probably have times when we struggle to commit ourselves to our local church with all its weaknesses, failures and frustrations. What can we do? We can pray for the same thing Paul does. Paul prays for Christians to keep trusting Jesus and that God would give them the joy, the peace and the hope they need in order to love one another like he loves them. Jesus was willing to go through brutal torture and death for the sake of his people. How much is the average Christian willing to endure before they give up on their spiritual family? As a Christian, I need to pray Paul's prayer for myself so that God would give me the strength to be humble and keep loving my church family rather than complain or walk away.