"Rejoice with those who rejoice; mourn with those who mourn. Live in harmony with one another." — Romans 12:15-16
Wise believers acknowledge that when Jesus said, "A new command I give you: Love one another" (John 13:34), this was not simply a suggestion for getting along. So too, the Bible's commands as to how we treat one another shouldn't be considered optional. That's not the nature of God's commands.
As Christ's followers, we must remember how our relationship with God affects our relationships with each other. When we pray, "Our Father," we acknowledge that we are part of a family that includes sisters and brothers. We're called to live in harmony together. Today's reading mentions specific ways of doing so, such as honoring one another above ourselves, holding to what is good, praying faithfully, sharing with people in need, showing hospitality, and not being proud.
When believers live in harmony, expressing their love for one another by sharing tears in times of sorrow and expanding their joy by celebrating together, they become appealing witnesses to their hope in Christ. When a coworker observes, "It's amazing how you guys love each other," the cause of Christ moves forward. Jesus taught this when he prayed that all believers "may be one" and "may be brought to complete unity. Then," he said to the Father, "the world will know that you sent me and have loved them even as you have loved me" (John 17:22-23).