I John 5:7 “For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one.”
The “witness of God” (I John 5:9) is explained in I John 5:6-9. In verse six, it is “the Spirit that beareth witness”; in verse seven, it is “the Father, the Word, and the Holy Ghost” that “bear record in heaven” (same as “witness”); and in verse eight, it is “the Spirit, and the water, and the blood” “that bear witness in earth”. In each of these verses the “witness” is giving testimony that Jesus Christ, our Savior, our Lord, and our Master is the Son of God. I John 4:7 and the word Triune signify that there are “three” that “are one”. God reveals Himself to us as “the Father, the Word, and the Holy Ghost”. Jesus plainly tells us that He “came forth from the Father” (John 16:28) and refers to “the glory which” He “had with” His Father “before the world was” (John 17:5). When our Lord was Baptized, all Three Persons of the Godhead were revealed; Jesus the Son of God was being Baptized, “the Spirit of God” descended “like a dove, and lighting upon him”, and God the Father said, “This is my beloved Son, in whom I am well pleased” (Matthew 3:17). There have been many natural illustrations used to explain how “three” can be “one”; but, none seem to fully explain it. Such a thing is extremely complex to our natural minds; for example, our Lord told His Disciples, “he that hath seen me hath seen the Father” (John 14:9); yet, The Son of God “prayed, saying, O my Father” (Matthew 26:39). I am satisfied in my soul that “there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one” and that God reveals Himself in various functional ways as “the Father, the Word, and the Holy Ghost”. Thus, our God is perfect and complete in every way; He reveals His Perfection in His Eternal Sovereignty; in His Power, Authority, and “great love wherewith he loved us” (Ephesus 2:4). His love is so sure that nothing “shall be able to separate us from the love of God, which is in Christ Jesus our Lord” (Romans 8:39). Thus, we are greatly comforted, and we daily rejoice, “For as many as are led by the Spirit of God, they are the sons of God.” (Romans 8:14).