It is the Spirit that beareth witness, because the Spirit is truth.
1 John 5:6
I wonder if any Christian can ever show forth the transforming radiance of the love of God without a complete surrender to the indwelling Person of the Holy Spirit.
Surely that was in the mind of the songwriter, as he prayed and sang:
Holy Ghost, with light divine,
Shine upon this heart of mine;
Chase the shades of night away,
Turn my darkness into day.
Holy Spirit, all divine,
Dwell within this heart of mine;
Cast down every idol throne,
Reign supreme—and reign alone.
Our world is filled with hatred and conflict, violence and bloodshed. Through the plan of redemption, God has dealt graciously with this global problem of hatred in the hearts of men and women. He has sent the source of love and light and radiance to the human bosom; Paul himself testifying: “The love of God is shed abroad in our hearts by the Holy Ghost which is given unto us” (Romans 5:5).
Lord, may Your divine love minister through me to a hurting person today.
The Father also testified to the Son through the ministry of the Spirit, who is the truth (cf. John 14:17; 15:26; 16:13). The Holy Spirit is the Spirit of truth in that He is true and, therefore, the source and revealer of divine truth (1 Peter 1:12; cf. Acts 1:16; 28:25; Heb. 3:7; 10:15–17), particularly about Jesus Christ (John 15:26). The Spirit was involved at Jesus’ conception (Matt. 1:18, 20; Luke 1:35), baptism (Matt. 3:16), temptation (Mark 1:12; Luke 4:1), and throughout His ministry. Peter said to those gathered in Cornelius’s house, “You know of Jesus of Nazareth, how God anointed Him with the Holy Spirit and with power, and how He went about doing good and healing all who were oppressed by the devil, for God was with Him” (Acts 10:38; cf. Matt. 12:28; Luke 4:14; John 3:34). Because the Holy Spirit empowered Jesus for ministry, to attribute Christ’s miraculous works to Satan was to blaspheme the Holy Spirit (Mark 3:28–30). Jesus always did the will of the Father in the power of the Spirit.
John continues, “And it is the Spirit who testifies, because the Spirit is the truth.” The word testify is rather significant in this paragraph. The Spirit is testifying as a witness to the birth (Matt. 1:20 [conception]; Luke 1:35; 2:25–32), baptism (Matt. 3:16; Luke 3:22), teaching (John 6:63), and ministry of Jesus (Luke 4:1, 18). John affirms the words of Jesus: “When the Counselor comes, whom I will send to you from the Father, the Spirit of truth who goes out from the Father, he will testify about me” (John 15:26). The Spirit continues to testify to God’s truth with reference to the person and work of Jesus.
John states the reason for the testifying work of the Spirit. He writes, “Because the Spirit is the truth.” John identifies the Spirit with the truth and alludes to the words of Jesus, “I am … the truth.” That is, both Jesus and the Spirit have their essence in the truth. The Spirit testifies because of his identity with the truth in Jesus.
“For there are three that testify: the Spirit, the water and the blood.” Of the English-language translations, only two (KJV, NKJV) have the expanded verses (vv. 7–8). “For there are three who bear witness in heaven: the Father, the Word, and the Holy Spirit; and these three are one. And 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 Testaments (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 the testimony of two or three witnesses.”
It is the Spirit who bears witness, because the Spirit is truth. This means that the Holy Spirit of God always testifies to the truth concerning the Lord Jesus which John has been unfolding. He bears witness that Christ came not with water only, but with water and with blood, because this is the truth of God.
 Tozer, A. W. (2015). Mornings with tozer: daily devotional readings. Chicago, IL: Moody Publishers.
 MacArthur, J. (2007). 1, 2, 3 John (p. 195). Chicago, IL: Moody Publishers.
 Kistemaker, S. J., & Hendriksen, W. (1953–2001). Exposition of James and the Epistles of John (Vol. 14, pp. 353–354). Grand Rapids: Baker Book House.
 MacDonald, W. (1995). Believer’s Bible Commentary: Old and New Testaments. (A. Farstad, Ed.) (p. 2323). Nashville: Thomas Nelson.