Summary: 1) The Eternal Truth in the Old Light (1 John 2:7), 2) The Eternal Truth in a new Light (1 John 2:8) 3) The Eternal Truth as a Way of Life (1 John 2:9-11)
There is an interesting feature often prevalent in looking at old photographs. Even when we look at people we don’t know, we can often tell a lot about the relationship. We can see if the people are open with each other and how close they are. That closeness, or fellowship, is very rarely faked. If it is, like in a fake smile for a picture, it is very quickly determined as to its genuineness once the camera is taken away.
Fellowship with God (is the essence of being in the Light). Heretics claim it, but their claim is a lie as John proves decisively. He and his readers have it; John proves that statement and even shows how they know beyond a doubt that they have it. But having fellowship with God means also that John and his readers have fellowship “with one another.” (Lenski, R. C. H. (1966). The interpretation of the epistles of St. Peter, St. John and St. Jude (411). Minneapolis, MN.: Augsburg Publishing House.)
Too often we think of Christian maturity in terms of freedom from sin. Provided that we think of sins of omission rather than commission, that is fair enough. But John wants us to see that spiritual life is characterized by positive acts of love, and that such love will be seen in the fellowship of the church as well as in our attitude to other people generally... The gospel is about “faith expressing itself through love” (Gal. 5:6), and anything else is counterfeit (Marshall, I. H. (1978). The Epistles of John. The New International Commentary of the New Testament (133). Grand Rapids, MI: Wm. B. Eerdmans Publishing Co.).
In 1 John 2:7-11 we see the description of the fellowship in love as: 1) The Eternal Truth in the Old Light (1 John 2:7), 2) The Eternal Truth in a new Light (1 John 2:8) 3) The Eternal Truth as a Way of Life (1 John 2:9-11)
1) The Eternal Truth in the Old Light (1 John 2:7)
1 John 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. (ESV)
Throughout the centuries preachers, teachers, and commentators have called John “the apostle of love.” His love to fellow believers to whom he wrote often expressed itself by the familiar term beloved (cf. 3:2, 21; 4:1, 7; 3 John 2). That title was so appropriate in this epistle, which affirms love as the benchmark of true salvation.
John’s love for his readers prompts the address “beloved”; and he now asks them to remain in the fellowship of mutual love (Lenski, R. C. H. (1966). The interpretation of the epistles of St. Peter, St. John and St. Jude (412). Minneapolis, MN.: Augsburg Publishing House.).
In this context the reference to John’s readers as “beloved” is entirely suitable. Before he mentions the commandment of love, he puts it into practice (Smalley, S. S. (2002). Vol. 51: Word Biblical Commentary : 1,2,3 John. Word Biblical Commentary (54). Dallas: Word, Incorporated.).
In the Pentateuch, God established the law of love in unmistakable terms:
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. (ESV)
The concept neighbor included the fellow Israelite and the alien who lived with God’s people in the land. In New Testament times, however, Jesus gave new meaning to the command to love one’s neighbor when he taught the Parable of the Good Samaritan (Luke 10:25–37) and when he told his listeners that the command to love one’s neighbor extended even to the enemy (Matt. 5:43–44).
He explained the meaning of the command to love one another by removing manmade obstacles and by revealing the divine intent and purpose of this particular command (Kistemaker, S. J., & Hendriksen, W. (1953-2001). Vol. 14: New Testament commentary : Exposition of James and the Epistles of John. New Testament Commentary (260). Grand Rapids: Baker Book House.)
Please turn to Romans 13
In a play on words, extended into verse 8, John wrote that the commandment to love was not a new commandment in one sense, but actually an old commandment. It had been taught throughout the biblical text. Whether they were Jews or Gentiles, John’s readers would have heard from the Old Testament about the concept of loving one another (1 Sam. 20:17, 41–42; cf. Gen. 45:15; Ps. 133:1–2).
Instructing the Romans concerning brotherly love, Paul quoted the Decalogue and Leviticus 19:18:
Romans 13:8-10 Owe no one anything, except to love each other, for the one who loves another has fulfilled the law. For the commandments, "You shall not commit adultery, You shall not murder, You shall not steal, You shall not covet," and any other commandment, are summed up in this word: "You shall love your neighbor as yourself." Love does no wrong to a neighbor; therefore love is the fulfilling of the law. (ESV) (cf. John 13:34–35; 1 Cor. 14:1; Phil. 1:9; Col. 3:14; 1 Thess. 4:9; 1 Tim. 2:15; Heb. 6:10; 1 Peter 1:22; 4:8; 1 John 3:23; 4:7, 21)