“Love one another” is not a suggestion. It is not an option for a Christian. It cannot be placed on a list of “gray areas.” Good Christians do not hold varying interpretations on this matter that are debated in public forums or book series. There are no good Christians who do not love one another; there are no Christians who do not love the brethren.
Few things can be more black-and-white than this. Just as belief in Christ is the necessary article of faith, loving the brethren is the first and necessary fruit of salvation. John’s terms cannot be more crystal clear: whoever loves his brother abides in the light (2:10), the one who does not love his brother is not of God (3:10), whoever does not love abides in death (3:14), whoever loves has been born of God and knows God (4:7) but the one who does not love does not know God (4:8), and, “If anyone says, ‘I love God,’ and hates his brother, he is a liar; for he who does not love his brother whom he has seen cannot love God whom he has not seen” (4:20).
Loving the brethren is a non-negotiable matter for the Christian. May Christ’s command to us expose sins which must be repented of, yet reveal to us the fruit that brings assurance.