Paul's life radically changed when he encountered Jesus. He preached the good news of salvation through Jesus to people both near and far. God's love changed Paul, and he wanted to encourage the believers in Rome that they shouldn't just act like everyone else in the culture. When we follow Jesus, God's love changes us too.

Romans 12:1-2 says:

I appeal to you therefore, brothers, by the mercies of God, to present your bodies as a living sacrifice, holy and acceptable to God, which Is your spiritual worship. Do no be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect.

These verses are telling us to give our whole lives to God and to not let the world shape how you think or act. God transforms (or changes) us when we place our faith in Jesus and follow him.