4. In spite of the fact that the third of these explanations fits the context well and is otherwise commendable, it is possible that still another view is involved. It must be remembered that in this context John is talking about the witness of the Father to Jesus, much as Jesus Himself does in the discourse recorded in John 5, and that it is hard to see how this can be adequately done without reference to the Scriptures in which that testimony is given most completely. Indeed, in John 5 the greatest place is given to a discussion of God’s witness through the Scriptures (vv. 37-47), even though other witnesses are mentioned. If this is so, however, we ask ourselves at what place in this passage such a witness is involved and answer that the only place at which it can be involved is in the word “water,” which is, in fact, used as a symbol for the Word of God elsewhere (Psa. 119:9; Eph. 5:26; John 15:3).
Can “water” symbolize the Scriptures at this point? It is not impossible. Besides, if this is the case, then the threefold witness of the Father to Jesus in verse eight becomes a witness which involves each member of the Trinity. “Spirit” refers to the Holy Spirit’s witness within the individual, “blood” to the historical witness of Christ’s death as the focal point of His ministry, and “water” to God the Father’s unique witness to Christ through the inspired Scriptures. To reject these three would be therefore truly to reject God’s witness and to call the only true and triune God a liar (v. 10).
John’s emphasis upon the fact that there are three witnesses and that the witnesses agree recalls the important Old Testament principle: “At the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established” (Deut. 19:15; cf. Num. 35:30; Deut. 17:6-7).
John has outlined the nature of the testimony of the Father to Jesus and is about to go on to summarize that testimony in order to provide a proper ending to the letter. But before he goes on he pauses to show why the divine testimony should be believed. There are two reasons: first, because it is greater than human testimony which all people accept (at least at times) and, second, because willful unbelief is sin.
John argues from our willingness to accept human testimony (which we all know is fallible) to our obligation to accept the testimony of God. Men and women accept the witness of other human beings every day of their lives. Otherwise they would not be able to sign a contract, write a check, pay a bill, buy a ticket, ride a bus, or do any of the other thousand things that constitute daily living. Well, then, says John, why should they not believe God, whose word alone is absolutely trustworthy?
If a person does believe God, he has an internal assurance that what he has believed is trustworthy. This is the work of God’s Spirit, the testimonium Spiritus Sancti internum, as the Reformers termed it. It is in addition to the assurance provided on other grounds. On the other hand, if a person does not believe God, he makes Him out to be a liar; for in this way he eloquently testifies to his belief that God cannot be trusted. Here the heinous nature of unbelief is evident. For, as Stott writes, “Unbelief is not a misfortune to be pitied; it is a sin to be deplored. Its sinfulness lies in the fact that it contradicts the word of the one true God and thus attributes falsehood to him.”1
1John R. W. Stott, The Epistles of John (Grand Rapids, MI: Eerdmans, 1964), 182.