This is my commandment, that ye love one another, as I have loved you. – John 15:12
In this verse our Lord returns to the old lesson which He has taught before: the great duty of love towards other Christians. He backs the command by His own example. Nothing less than His matchless love towards sinners should be the measure and standard of love to one another.
The frequent repetition of this command teaches the vast importance of Christian charity, and the great rarity of it. How anyone can pretend to Christian hope who is ignorant of Christian love, it is hard to understand. He that supposes that he is right in the sight of God because his doctrinal views are correct, while he is unloving in his temper, and sharp, cross, snappish, and ill-natured in the use of his tongue, exhibits wretched ignorance of the first principles of Christ’s Gospel. The crossness, spitefulness, jealousy, maliciousness, and general disagreeableness of many high professors of “sound doctrine” are a positive scandal to Christianity. Where there is little love there can be little grace.
– Expository Thoughts on John, J.C. Ryle (1873)