“For there are three that bear record [in heaven, the Father, the Word, and the Holy Ghost: and these three are one. And there are three that bear witness in earth,] the spirit, and the water, and the blood: and these three agree in one.”
One scripture that is often presented to support the trinity is 1 John 5:7,8. I believe the evidence is overwhelming that the part in brackets above were never written by John, but are in interpolation. I have no doubt that John did not write the words as they appear in the King James Version and some other translations in 1 John 5:7, but these words, even as they appear in the KJV, do not say anything at all about three persons in one God, nor three aspects of God, nor three modes of God, etc. One has to add the trinitarian (or modalist) doctrine to the words and then read the doctrine into the words, even as they appear in the KJV.
Thus there is nothing at all in 1 John 5:7,8, even in the KJV, that offers any proof of the trinity, that is, three separate and distinct sentient/ominscient persons in one ominiscient being, or modalism, that is, the belief that God is one person who has revealed himself in three forms or modes (Father, Son, Spirit), all three modes being the one God.
The general presentation of what God has revealed through the holy spirit throughout scriptures is that the only true God sent Jesus, not that Jesus is the only true God who sent Jesus. The holy spirit reveals through the scriptures that Yahweh (Jehovah) is the only true God, the God and Father of the Lord Jesus and that Yahweh (Jehovah) is the God and Father of the Lord Jesus. Jesus has one who is the Supreme Being over him; Jesus is not his Supreme Being whom he worships, prays to, and who sent him, and whose will he carried out in willful obedience. — Deuteronomy 18:15-19; Matthew 4:4 (Deuteronomy 8:3; Luke 4:4); Matthew 4:7 (Deuteronomy 6:16); Matthew 4:10 (Exodus 20:3-5; 34:14; Deuteronomy 6:13,14; 10:20; Luke 4:8); Matthew 22:29-40; Matthew 26:42; Matthew 27:46; Mark 10:6 (Genesis 1:27; Genesis 2:7,20-23); Mark 14:36; 15:34; Luke 22:42; John 4:3; 5:30; 6:38; 17:1,3; 20:17; Romans 15:6; 2 Corinthians 1:3; 11:31; Ephesians 1:3,17; Hebrews 1:9; 10:7; 1 Peter 1:3; Revelation 2:7; 3:2,12.
As far as 1 John 5:7 is concerned, the word “hen” — translated “one” — is neuter, and thus its application would have to be a neuter “one”. The trinitarian phrases “treis hypostaseis en mia ousia”, (“three persons in one substance”), or “mia ousia, treis hypostaseis” (“One essence in three persons”), cannot be what is being referred to, since the Greek word “ousia” is not neuter, but feminine, thus as shown in the phrases, the Greek word “mia” is used, not “hen”.
Likewise, “theos” (three in one God) is masculine and would require the Greek word heis, as appears in 1 Corinthians 8:6 as “heis theos” (one God).
Believing that God has not left us without a testimony concerning this, we seek to compare spiritual revealment with spiritual revealment. (1 Corinthians 2:10,13) We see a similar testimony in John 17:11,21,22. Here Jesus prays for the his followers to be one with him, one with his Father, and one with each other. He uses the Greek word “hen” in each usage. Jesus certainly did not pray that they be all one being or one God, which would be nonsense, but that their unity may be one in mind, heart and will. Since the oneness for which He prayed for them was not a oneness of being or oneness of nature as the Supreme Being, the oneness between Him and the Father cannot be that of being, because Jesus in John 17:11,22 prays that the oneness for which He prayed on their behalf be patterned after the oneness that exists between the Father and himself: “That they may be one as we are.” Hence the oneness between the Father and Jesus is not one of being, nor as one God, but one of mind, heart and will. Moreover Jesus defines this oneness in verse 21 as follows: “that they all may be one, as thou, Father, art in me [Yahweh was in Jesus by his holy spirit, (John 14:17,20) and I in thee [Jesus was in the Father (John 14:10,11,20) by accepting and keeping the Father as his head, i.e,, by his being and remaining in the consecrated attitude].
Regardless, there is nothing, even in the KJV, in 1 John 5:7 about the trinity doctrine, nor the modalist doctrine.