There is nothing novel or unprecedented, then, about John’s teaching that Christians are marked by love for one another. (His teaching about love in this epistle serves as the second aspect of the moral test – cf. 2.7-11). Because God loves them (Romans 5.8; Ephesians 1.13-14; 2:4-5), true believers will surely reflect that love in their relationships with other people (Matthew 22.37-39; Ephesians 5.2; 1 John 4.9). Thus, the apostle’s instruction here is not new, but is “an old commandment, which you have had from the beginning; the old commandment is the word which you have heard” (2.7; cf. verse 10; 4.7-8).
John’s readers knew that truth because apostolic preachers had faithfully delivered it to them (cf. 1.5; 2.24). However, false teachers had also come and taught, apparently, that brotherly love is not an essential mark of true salvation. Those apostates added to their erroneous view of Christ’s nature and their disobedience to God’s commands a lack of love for true believers. In response, John directed his readers back to “the message” they had “heard from the beginning,” referring to the beginning of gospel proclamation. That teaching included the truth about Jesus Christ, the gospel, mankind’s sinful condition, and the need for righteous living, as well as the command to “love one another.” The apostle urged his readers to remember what they were first taught and not allow anyone to lead them astray (cf. Jude 3).
From: The MacArthur New Testament Commentary: 1-3 John by John MacArthur (Chicago: Moody Press, 2007), p. 131. Comment on 1 John 3.11-18.
John Fullerton MacArthur, Jr. (born in 1939) has been Senior Pastor of Grace Community Church of the Valley, in Sun Valley, California, since 1969. On Sunday, June 5, 2011, having preached from Mark 16.1-8, the congregation celebrated the completion of MacArthur’s 42-year-long project: to preach through the entire New Testament. (He still must preach through Mark 16.9-20, but the celebration took place after preaching the first 8 verses was completed, these being the last verses before those 12 ”disputed” verses at the very end of Mark’s gospel.)