In Romans 13, Paul continues his theme of marks of a true Christian and practically living the Christian life from chapter 12 to discussing the law of love and how it should govern the Christians’ relationships in two respects: in relation to government authorities, and then in relation to everyone else, more broadly.
We are commanded to submit to government authorities because God, in his sovereign and eternal wisdom, has instituted the powers that be for the good of all people. Because God is the one who has risen up these leaders, we are resisting God if we resist these authorities.
This does not mean, however, that there are never times a Christian can disobey the government. For example, if the government ever were to tell Christians to never share the gospel, the Christian would have an obligation to fulfill the commandment of God to go and make disciples of all nations (Matthew 28:19-20) rather than obey the government (see Acts 4:17-20, 5:27-29). The command of God always takes precedence over the command of man. No exceptions.
On the flip side, however, government is called not to abuse their authority, but to use it for the good of its people, and is actually meant to serve God and punish evil (Romans 13:4). So we see a command for both parties: Christians, obey the government, and government, use your power wisely.
Looking more broadly, Christians are called to love everyone because love fulfills the whole law and does not harm anyone (Romans 13:10). Love is not just some obscure, abstract term that we really don’t know what it means, but love is clearly defined all throughout the Bible, especially in places like 1 Corinthians 13 and Galatians 5:22-23. This is what it means to be a Christian, and by loving others well, we show the world to whom we belong, and that is Jesus Christ.
Love should always be on the forefront of out minds as Christians. If we are not loving, we are not living. Jesus said that the world will know that we are his disciples if we love one another; what better time is there to start doing this then now?