1 John 2:7
 Beloved, I am writing you no new commandment, but an old commandment that you had from the beginning. The old commandment is the word that you have heard. (ESV)
The Apostle John is writing this letter to a church that was infiltrated by false teachers who were teaching that they had "new knowledge" that was superior to the Gospel taught by John. This so-called new knowledge taught that the spirit was everything and the body did not matter. Therefore, they felt that they did not need to worry about how they acted in their body toward one another. But, John reminds believers that a commandment to love one another is an old commandment that has not been discarded.
The Christian faith is all about what Christ has accomplished for us by his life, death, and resurrection. Jesus' perfect life included completely fulfilling the Old Testament Law. Remember, that Jesus did not come to abolish the Law, but to fulfill it. Part of the Law that the Apostle John would have been very familiar with, as well as his recipients of this letter, was found in Deuteronomy:
 You shall not take vengeance or bear a grudge against the sons of your own people, but you shall love your neighbor as yourself: I am the LORD. (ESV)
Jesus fulfilled the Law, including this command to love your neighbor as yourself. And if we are a part of Christ we are to have this very same love for our neighbors! John is saying, yes it is an old law, but it is still part of how a follower of Jesus lives. We must love one another.
How are you doing with this command? It's an old one, but a good one. We are to love one another. We are to love our neighbors. Lord Jesus, help us to love like you have loved us.