A clear and detailed explanation! This was discussed in our church and yeah, its within the context that John was speaking to the gnostics unbelievers. So, sin unto death (physical) or the spiritual death of an unbeliever.
1. So Gnostic unbelievers are encouraged to have fellowship with John, with true Christians, and with God!
That which we have seen and heard declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ.
2. So Gnostic unbelievers are promised a fulness of joy!
And these things write we unto you, that your joy may be full.
3. So Gnostic unbelievers are John's and God's little children!
My little children, these things write I unto you, that ye sin not.
4. So Gnostic unbelievers have an advocate with the Father, Jesus Christ the Righteous!
And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
5. So now Gnostic unbelievers can also be considered as Christian brethren!
Brethren, I write no new commandment unto you, but an old commandment which ye had from the beginning.
6. So Gnostic unbelievers have known Christ who is from the beginning!
I write unto you, fathers, because ye have known him that is from the beginning.
7. So Gnostic unbelievers have overcome the Wicked One!
I write unto you, young men, because ye have overcome the wicked one.
8. So Gnostic unbelievers are God's little children who have known God experientially!
I write unto you, little children, because ye have known the Father.
Do you see how heretical a teaching this is telling Christians that the first epistle of John was written to Gnostic unbelievers? This false doctrine has been going around for a while, and should be utterly rejected. All three of John's epistles are addressed to genuine believers, and the first epistle addresses sin in the believer's life.