"For there are three that testify: the Spirit, the water and the blook." Of the English-language translations, only two (KJV, NKJV) have the expanded verses (vv. 7-8). "For there are three that bear witness on earth" (NKJV). The translators of the New King James Version, however, state in a footnote that the Greek New Testament (Nestle-Aland, United Bible Societies, and Majority Text) "omit the words from 'in heaven' (v. 7) through 'on earth' (v. 8)." Only four or five very late Greek manuscripts contain these words.
John actually writes that three (Spirit, water, and blood) are testifying. But why does John place the historical facts of Jesus' baptism (water) and death (blood), to which the Spirit testifies, on the same level as the Spirit? How can water and blood testify along with the Spirit? We need to look at the text from a Semitic point of view. Impersonal objects can testify: for example, the heap of stones Jacob and Laban put together was called a witness (Gen. 31:48). And according to the Mosaic law (Deut. 19:15), "One witness is not enough.... A matter must be established by testimony of two or three witnesses."