I'm afraid I'm going to have to be firm here.
First John is not written to cause Christians to doubt their salvation.
There are just too many teachers out there using it that way; giving the idea that John's intention was to weed out the false professors from the true possessors of eternal life.
I don't question their motives. Many think the way to get Christians serious about living the Christian life is to whip them with the fear of Hell.
Number one, it's not correct Biblically; it's not "rightly dividing the Word of Truth," as Christ mandates.
Number two, it doesn't work. In fact, it often backfires and ends up shipwrecking the faith of some (believe me, I've seen it).
It's common to grab a verse here, and a text there, and say, "See, John says if you're not loving like Christ, then you're just not saved!"
I'm firmly convinced John is going the very opposite route.
You've got to look at the unity of the epistle; the WHOLE of the epistle, and weigh scripture with scripture to discern the Holy Spirit's true meaning, with a LOT of study and prayer, and not make sweeping statements based on a verse or verses wrested from their context.
John does not doubt that the people he's writing to have been born again.
He says, "I'm writing unto you because your sins ARE FORGIVEN;"
"I'm NOT writing unto you because you know not the truth, BUT BECAUSE YOU KNOW IT."
"Behold what manner of love the Father hath bestowed upon us, that we should be called THE SONS OF GOD;"
"Beloved, NOW ARE WE THE SONS OF GOD . . ."
His favorite way of addressing them?
"My little children" (literally, "my little born-ones"). Is this a title John would so freely use for unsaved people?
First John is the Risen and Ascended Lord Jesus expanding on truths He introduced in the Upper Room Discourse (John 13-17), particularly, the Vine and the Branches discourse (John 15), through the inspired pen of the Apostle John.
First John is about Christians, who HAVE new life, because they HAVE been born-again, walking in FELLOWSHIP with the Lord Jesus -- I John 1:3-4.
It is about believers and their need to ABIDE IN THE VINE.
It doesn't mean you're not born again if you don't love like Christ
(I mean, have you SEEN the way Jesus loves? Do you know ANYONE who consistently loves like that??? Do the teachers who preach this truly love like Christ even MOST of the time?? And those times when they FAIL to love like Christ -- does that mean they lose their salvation during that period of failure, and then get saved all over again when they manage to hit the standard once again??).
What makes you a born-again child of God is putting your faith in Jesus Christ for forgiveness of sins and the absolutely free GIFT of Eternal Life -- that, and that ALONE.
But, if you've been born again through faith in the shed Blood of Christ, and you're not loving like Him, it means you're not abiding in the Vine.
And John is all over that. He is all about ABIDING IN CHRIST, THE VINE.
The sad, ironic thing is this:
John's great premise is that everything we need IS IN THAT VINE (and ONLY in that Vine!).
He makes the firm point that the Love of God HAS to start WITH GOD.
Sorry, kids, but ain't none of us got that kind of love in ourselves! No -- not the Agape love that Paul talks about (I Cor. 13), and John talks about (I John 3:16-18) and that our sweet Lord Jesus completely, utterly embodies and personifies.
"We love Him because HE FIRST LOVED US."
"Herein is love: not that we loved God, but that He loved us . . ."
The strong teaching of First John is that, yes, only true, born-again children of God CAN love like that -- only the child of God has that capacity . . .
But only those children who continue on drinking from that rich flowing stream of God's love WILL ACTUALLY, ACTIVELY EXPRESS THE LOVE OF GOD to others.
In other words, in order to LOVE LIKE CHRIST, you first need to be rooted and grounded in His Amazing Love FOR YOU.
We believers draw our little rivulets of love from standing full in the torrent of His mighty, flowing RIVER of the Agape Love of God -- letting that powerful Tide hit us hard, wash over us, and drench us to our bones, until we're so soaked with it, it can't help but spill over as it keeps filling us to the brim.
Sorry again, but those who are sent out of the sanctuary seriously DOUBTING that they are even saved are NOT basking in God's incredible love FOR THEM. They're now ridden with anxiety and dread, feeling they may be lost and headed for Hell after all!
Not the right remedy, my brothers in Christ, for all your noble intentions.
John says, "We have known AND BELIEVED the Love that God hath to us. God is love; and he that dwelleth (abideth) in love dwelleth (abideth) in God, and God in him."
Back in the Vine and the Branches discourse (John 15), Jesus starts off ASSURING His disciples:
"Now ye are clean through the Word I have spoken unto you."
Then, note that Jesus FIRST says:
"As the Father hath loved me, so have I loved you: continue (again, same word as "abide") ye in my love."
KNOW THAT YOU ARE LOVED.
THEN, He says, "This is my commandment, That ye love one another -- AS I HAVE LOVED YOU."
The very painful thing is that, while John is strongly assuring the brethren, and telling them their outflow of love depends on their assurance of BEING loved . . .
So many teachers today grab a verse here, and a text there,
And rob believers of the very assurance Jesus gives them, and John says they so desperately NEED.
William R. Newell said, "The great secret is to BELIEVE; and to consent to being loved while unworthy."
Dearly BELOVED born-ones; Bask in the Love God has shed so abundantly on you. Believe it; Relish it; ABIDE in it.
Then, go out and let that only-one-of-its-kind LOVE flow right through you, the instrument, the channel, the vessel -- to the rest of the world.