And this is the [greatest] commandment [See Matt. 2:37-38] we have received from Him: [It requires] that the person who [claims to] love God should also love his brother.
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 as He has commanded us to do.
Now to summarize: All of you should think alike. Be sympathetically understanding [toward one another]. Be loving toward [your] brothers [and sisters]. Be tender-hearted and humble-minded.
[Since] you have purified your souls by [your] obedience to the truth [i.e., the Gospel message], which produces a genuine love for your brothers, [now] you should have this kind of fervent, heartfelt love for one another.
We ought to thank God for you always, brothers, since it is proper, because your faith is growing so much and the love that every one of you has for each other is increasing more and more.
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.