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Today begin a devotional study of 1 John. To introduce this New Testament book, I will answer six questions: Who wrote 1 John? What kind of book is it? When was it written? Where was it written to? Why was it written? And how does it apply to us today? 
First, who wrote 1 John? Formally speaking, 1 John is anonymous. But internal evidence indicates that the author was an eyewitness of Jesus Christ (1:1, 3; 4:14; 5:6-7). Additionally, the authoritative way he addresses his readers indicates that he was a leader of some standing within the church (e.g., 2:1-2, 8, 15, 17, 23, 28; 3:6, 9; 4:1, 8, 16: 5:21). The testimony of the early church is that the Apostle John wrote 1 John, and he certainly fits the bill of this internal evidence.
Second, what kind of book is it? Since the early church, 1 John has been referred to as a letter. However, it lacks a standard epistolary greeting and conclusion. Contrast it, in this regard, with 2 and 3 John, which have both. Nevertheless, it is a written communication of some sort. Notice how often John uses the verb “I write,” for example (2:1, 7, 8, 12-14, 21, 26). No doubt John’s readers received his communication through the mail, but it seems more like a sermon designed to read aloud than like a letter. Nevertheless, because of the long custom of the church, we will refer to 1 John as a letter.
Third, when was 1 John written? Just as the letter is formally anonymous, so it is also undated. However, various Christian documents from the late first and early second century allude to it, so it cannot have been written any later than then. Most commentators give 1 John a date sometime in the 90s. The Apostle John would have been an aged man by then. Perhaps this is why he refers to himself as “the elder” in 2 and 3 John.
Fourth, where was it written to? Again, nothing in 1 John itself indicates to whom John wrote this letter. However, just as early Christian documents enable us to specify an author and a date, so they help us specify a location. These documents consistently point to Ephesus and its environs as the location in which and to which 1 John was written.
Fifth, why was it written? According to 1 John 2:18-19, a group of false teachers had seceded from the church and was trying to convince other church members to do the same. Concerned about the spiritual danger of the situation, John wrote the church to warn it about “those who are trying to lead you astray” (verse 26). These false teachers made at least two errors: they denied the power of sin over their lives (1:6-10), and they denied that Jesus was the “Christ” who had come “in the flesh” (2:22 and 4:2 respectively). These are spiritually dangerous errors in the first and the twenty-first century.
And finally, how does it apply to us today? For an answer to that question, make sure to read tomorrow’s Daily Word!
 I am heavily dependent upon D. A. Carson and Douglas J. Moo, An Introduction to the New Testament, 2nd ed. (Grand Rapids, MI: Zondervan, 2005), 669-687, for my answers to these questions.