By this everyone will know that you are my disciples, if you love one another.
---John 13:34-35.
This is the ultimate mark of the believer. Its not the church or denomination. It's not a huge cross in someone's yard or the Christian radio station they always have on. Even baptism doesn't nessecarily make one a Christian. I know because I thought it was a free "get out of hell" card and was rebaptized when I was actually saved. I also listened to a sermon from my former pastor who had trouble getting a job when he first began ministry because some churches didn't think a pastor should have a beard. Many chuches now prefer a bearded pastor. But some believe a person's spiritual state can only be discerned by an outward display of holiness. This is no different from the Pharisees Jesus called the children of hell (Matthew 23:15).
Loving each other as Christ has loved us is an invisible sign of a Christian. But what does that mean?
Love is patient, love is kind. It does not envy, it does not boast, it is not proud.
It does not dishonor others, it is not self-seeking, it is not easily angered, it keeps no record of wrongs.
Love does not delight in evil but rejoices with the truth.
---1 Corinthians 13:3-8.
Love is secure, selfless, and doesn't keep score. Single people, pay attention. Never marry someone who brings up something you did two years ago.
Matthew 5:23-25 instructs us to seek reconcilliation while it is still in our power to do so. Sometimes, you are the person in need of forgiveness. Sometimes, you are the person who needs to administer forgiveness. Many times, you are both. We are also to confess our sins to each other (Jasmes 5:16). We need to confess anytime we have wronged someone and ask their forgiveness.
Whoever claims to love God yet hates a brother or sister is a liar. For whoever does not love their brother and sister, whom they have seen, cannot love God, whom they have not seen. And he has given us this command: Anyone who loves God must also love their brother and sister.
---1John 4:20-21.
In other words, it doesn't matter if you only listen to Christian music or engage in other outward signs of what you think a believer is supposed to do if you treat others like garbage. And yes, I have fallen short in all of these areas. I guess that's why it's so easy for me to write about it.