5:10 hath the witness. That internal witness is none other than the indwelling Holy Spirit, who is both “in heaven” (as the third person of the Godhead) and “in earth” (note I John 5:7-8), as He indwells each believer. Compare Romans 8:16-17; Galatians 4:6.

5:10 made him a liar. Those who recoil at the thought of eternal punishment of the lost need to reckon with the infinite magnitude of their sin—that of calling their own Creator a liar! An infinite sin warrants infinite punishment, especially in light of the infinite sacrifice made for them by their Creator and the free gift of infinite life (I John 5:11) offered them by that loving God on the basis of His sacrifice. The punishment is more than merited by the crime.

5:10 the record. The same Greek word, in either verb or noun form (martureo, marturia) is translated “record” three times in this epistle, “testify” twice, and “witness” seven times. These words are also very common in John’s other writings. The frequent cost of such a “witness” is pointed up by the fact that we derive our word “martyr” from this Greek word.

5:12 hath life. The same division is stressed in John 3:18,36; Daniel 12:2; Matthew 7:13-14; 25:46; Revelation 21:6-8; 22:14-15; and others.

5:13 that ye may know. The most definitive basis for our assurance of salvation is true faith in “the name of the Son of God,” with whatever that entails. John has also given a number of tests for knowing that our faith in Him is true faith, not just mental assent to a tenet of faith. Such tests are noted in I John 2:3; 2:5; 2:6; 2:29; 3:2,3; 3:14; 3:18,19; 3:24; 4:13; 5:2. Compare also John 20:31.