“Be devoted to one another in brotherly love; give preference to one another in honor.” Romans 12:10 (NASB)
“Brotherly love is one of the marks by which the world will know that we belong to Christ. ‘By this all men will know that you are My disciples, if you have love for one another’ (John 13:35). This love is not optional for believers. It not only is required but is inescapable, because ‘whoever loves the Father loves the child born of Him’ (1 John 5:1). In fact, as John has just declared, ‘If someone says, “I love God,” and hates his brother, he is a liar; for the one who does not love his brother whom he has seen, cannot lover God whom he has not seen’ (4:20).” 
“Christian fellowship is much more than a pat on the back and a handshake. It means sharing the burdens and the blessings of others so that we all grow together and glorify the Lord. If Christians cannot get along with one another how can they ever face their enemies.” 
For the one who believes in the infinite love of God, it becomes natural for him to live a life of love. Brotherly affection is opposed to self-seeking pride and it honors others. It impels men and women to cultivate that spirit of love springing from a fellowship with God in Christ.
. John MacArthur, Commentary, Romans 9-16
. Warren W. Wiersbe, Be Right