The capacity for love

The capacity for love gives depth to human relationships, brings people closer to each other physically and emotionally, and makes people think expansively about themselves and the world.  In his triangular theory of love, psychologist Robert Sternberg theorizes that love is a mix of three components: some (1) passion, or physical attraction; (2) intimacy, or feelings of closeness; and (3) commitment, involving the decision to initiate and sustain a relationship.  The presence of all three components characterizes consummate love, the most durable type of love.  In addition, the presence of intimacy and passion in marital relationships predicts marital satisfaction.  Also, commitment is the best predictor of relationship satisfaction, especially in long-term relationships.  Positive consequences of being in love include increased self-esteem and self-efficacy.[4]

The Bible records why Christians should love one another :-

1) God has commanded us to love (1 John 2:7-11)

2) We have been born of God and God's love lives in us (1 John 3:10-24)

3) God first revealed His love to us (1 John 4:7-21)

"We love ... because He first loved us."

What happens to a believer who does not love the brethren? 

1) he lives in darkness, though he thinks he is living in the light (1 John 2:9).  He thinks he sees, but he is actually blinded by the darkness of hatred.

2) he becomes a cause of stumbling (cf. 1 John 2:10).

an unloving brother stumbles himself, and in addition he causes others to stumble.  The best way to help other Christians not to stumble is to love them. Love makes us stepping-stones; hatred (or any of its "cousins," such as envy or malice) makes us stumbling blocks.

3) it retards a believer's spiritual progress (1 John 2:11).