By this all people will know that you are my disciples, if you have love for one another. John 13:35
“Let us note that our Lord does not name gifts or miracles or intellectual attainments as the evidence of discipleship, but love, the simple grace of love, a grace within reach of the poorest, lowliest believer, as the evidence of discipleship. If we have no love, we have no grace, no regeneration, no true Christianity! . . .
Let us note what a heavy condemnation this verse pronounces on sectarianism, bigotry, narrow-mindedness, party-spirit, strife, bitterness, needless controversy between Christian and Christian.
Let us note how far from satisfactory is the state of those who are content with sound doctrinal opinions and orthodox correct views of the Gospel, while in their daily life they give way to ill temper, ill nature, malice, envy, quarreling, squabbling, bickering, surliness, passion, snappish language, and crossness of word and manner. Such persons, whether they know it or not, are daily proclaiming that they are not Christ’s disciples. It is nonsense to talk about justification, and regeneration, and election, and conversion, and the uselessness of works, unless people can see in us practical Christian love.”
J. C. Ryle, Expository Thoughts on the Gospels, on John 13:34-35.