What does it mean that there are three that bear record (1 John 5:7)?

John writes chapter 5 of his first letter to encourage believers by providing them assurance of their position in Christ—a position that is eternally secure. He explains that he has written to those who have believed in Jesus so that they may know (or understand with certainty) that they have (in the present tense) eternal life (1 John 5:13). John emphasizes in this context that there are “three that bear record in heaven” (1 John 5:7, KJV). That threefold testimony affirms that the believer in Jesus Christ indeed has eternal life.

John begins this section of his epistle by asserting that the one believing that Jesus is the Christ is born of God and is loved by God the Father (1 John 5:1). If God loves His children, then His children ought also to love God’s children. Believers can know they are loving God’s children by obeying what He told them to do (1 John 5:2)—by expressing that love as God has designed. God’s instructions are not burdensome or too difficult to obey (1 John 5:3). John reminds believers that they have already overcome the world by their faith in Christ (1 John 5:4), because all who have believed in Jesus have overcome the world (1 John 5:5). John appeals to important witnesses to this fact, stating that “there are three that bear record in heaven” (1 John 5:7, KJV).

In John 5:6a, John explains that Jesus came by water and by blood—emphasizing that to Jesus’ human birth was added His perfect and sinless blood, enabling Him to be the substitute for sin. John points to the Spirit of God who testifies to this fact, and His word can be trusted (1 John 5:6b). In fact, John affirms that there are three that bear record (1 John 5:7). And this is where we have some differences in the various translations.

The KJV specifies that the “three that bear record in heaven” are the Father, the Word, and the Holy Ghost, and that those three are one (1 John 5:7). In the next verse, the KJV says, “There are three that bear witness in earth, the spirit, and the water, and the blood,” and that these three agree (1 John 5:8). Other translations (like the ASV, NASB, ESV, etc.) do not contain the heaven-and-earth phrases and note that the three that bear record are the Spirit, the water, and the blood (1 John 5:7–8). These three witnesses agree that Jesus is God come in the flesh (e.g., 1 John 4:2).

First John 5:7–8 is thus an example of a textual variant (the KJV was translated from different manuscripts than were the ASV, NASB, ESV, etc.). Depending on which translation is read, the reader will understand that either there are six witnesses:
or there are three witnesses:
In either of these readings, God bears record that Jesus is the Christ, the Son of God. Consequently, the one who has believed in Jesus is secure in his or her salvation, as God also bears witness that the believing one has eternal life (1 John 5:10–13).