1J 2:7b old commandment was the new commandment in 1J 2:8a

[tonychanyt]

Leviticus 19:

18 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.

Jesus updated that love in John 13:

34 "A new commandment I give to you, that you love one another: just as I have loved you, you also are to love one another."

The old love commandment: Love your neighbor as yourself.
The new love commandment: Love one another as Jesus loves you.

Jesus didn't abolish the old love commandment but fulfilled it, renewed it, and upgraded it to the new. It was called new because Jesus demonstrated the new standard for love. He was the new standard.

Six decades later, John recalled this teaching in 1J 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.

By now, Jesus' new commandment to love was well-known among believers. They had heard it many times already. John, now, called it an old commandment. However, not to confuse it with Le 19:18b, John elaborated:

8 At the same time, it is a new commandment that I am writing to you,

That's what Jesus called a new commandment earlier.

which is true in him [Christ] and in you, because the darkness is passing away and the true light is already shining.

true light in Christ

9 Whoever says he is in the light and hates his brother is still in darkness.

Jesus called believers to love one another with his love. You shouldn't hate your brother.

In this passage, John discussed the same love commandment in J 13:34. It was new when Jesus commanded it. Six decades later, John referred to it as an old commandment in 1J 2:7.