Mission and acceptance of others (Romans 15)

Paul writes to the Christians in Rome about his missions to the Gentiles and his plans to visit them on the way to Spain.

(1) What does Romans 15 teach us about God?

(2) What does it teach us about human nature?

(3) What does it teach us about our responsibilities as Christians?

(4) In one sentence, sum up what this passage teaches us about mission?