Rom 12:16-18, 16 Live in harmony with one another…17 Repay no one evil for evil, but give thought to do what is honorable in the sight of all. 18 If possible, so far as it depends on you, live peaceably with all.
In music, harmony is the combination of simultaneously sounded musical notes to produce chords pleasing to the ear. Though instruments are different, well tuned in skillful hands, working in agreement will produce a masterpiece.
Blessed are the peacemakers, those who aspire to live in harmony (in agreement) (Mat 5:9), meaning they out of love for God and man will do all possible good to all men. There are times of conflicts as Jesus warned but with biblical counsel, we learn to forgive, resolve and reconcile.
To live in harmony, one must aspire to have the fruit of the Spirit, a means to contentment. Gal 5:22-23, “22 But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, 23 gentleness, self-control; against such things there is no law.” A person who murders lacks the 9 fruit of the Spirit listed above and Jesus said, if you hate your brother, you are a murderer at heart and you are not a peacemaker. Live in harmony with one another.