1 John 2:7

My dearly loved ones, I am not writing to you about a new commandment, but about an old one. [It is the one] you had learned about from the beginning. [Note: This is the commandment to love one another (3:1: II John 5) which Jesus had taught his disciples during His earthly ministry. See Mark 12:31]. This old commandment is the word [of God] which you heard [previously].

1 John 3:11

[Now] this is the message that you people heard from the beginning [of Christ's ministry], that we should love one another [See Mark 12:31],

2 John 1:5-6

And now I ask you, lady [See verse 1], not as though writing a new commandment to you, but [I wanted to remind you of] one that we had [heard] from the beginning [of Christ's ministry]: [It is] that we should love one another.

Matthew 5:43

"You have heard what was said [Lev. 19:18], 'You must love your neighbor and hate your enemy.'

Matthew 22:37-40

Jesus replied, [Deut. 6:5] "'You must love the Lord your God with all your heart, with all your soul and with all your mind.'

Mark 12:29-34

And Jesus answered, "The foremost one is this [Deut. 6:4-5], 'Hear this, you Israelites, the Lord our God is the only Lord,

Acts 17:19

So, they led him to the Areopagus [i.e., an elevated assembly place called "the Hill of Mars"] and asked him, "Could we learn [more] about this new teaching you are speaking of?

Romans 13:8-10

Do not owe anything to anyone, except to love one another. For the person who loves others has fulfilled [the requirements of] the law.

Galatians 5:13-14

For you brothers were called [by God] to enjoy your freedom; but do not use this freedom as an excuse for living a sinful life; instead, use it to render loving service to each other.

James 2:8-12

However, you are doing well if you fulfill [i.e., obey] the royal law found in the Scriptures [Lev. 19:18], "You should love your neighbor the same way that you love yourself."

1 John 2:24

You people should continue [to practice] what you heard from the beginning [i.e., to love one another, See verses 7-11]. If you do, then you also will continue in [fellowship with] the Son, and with the Father.

1 John 3:23

And this is His commandment: We should believe in the name of His Son Jesus Christ [i.e., the person of Christ], and love one another, just He has commanded us to do.

Treasury of Scripture Knowledge

Summary

Brethren, I write no new commandment unto you, but an old commandment which ye had from the beginning. The old commandment is the word which ye have heard from the beginning.

General references

Bible References

I write

1 John 3:11
[Now] this is the message that you people heard from the beginning [of Christ's ministry], that we should love one another [See Mark 12:31],
Acts 17:19
So, they led him to the Areopagus [i.e., an elevated assembly place called "the Hill of Mars"] and asked him, "Could we learn [more] about this new teaching you are speaking of?
2 John 1:5
And now I ask you, lady [See verse 1], not as though writing a new commandment to you, but [I wanted to remind you of] one that we had [heard] from the beginning [of Christ's ministry]: [It is] that we should love one another.

But

Matthew 5:43
"You have heard what was said [Lev. 19:18], 'You must love your neighbor and hate your enemy.'
Matthew 22:37
Jesus replied, [Deut. 6:5] "'You must love the Lord your God with all your heart, with all your soul and with all your mind.'
Mark 12:29
And Jesus answered, "The foremost one is this [Deut. 6:4-5], 'Hear this, you Israelites, the Lord our God is the only Lord,
Romans 13:8
Do not owe anything to anyone, except to love one another. For the person who loves others has fulfilled [the requirements of] the law.
Galatians 5:13
For you brothers were called [by God] to enjoy your freedom; but do not use this freedom as an excuse for living a sinful life; instead, use it to render loving service to each other.
James 2:8
However, you are doing well if you fulfill [i.e., obey] the royal law found in the Scriptures [Lev. 19:18], "You should love your neighbor the same way that you love yourself."

General references

John 15:12
My commandment [to you] is this: You should love one another just as I have loved you.