Jesus Christ is the revelation of the Word of God in human form, and the entire Bible (in the words of Karl Barth) is a human witness to Jesus Christ who is the very Word of God. Many Christians wrongly identify the Bible as the Word of God, but the Bible is only a book that has an indirect identity with Jesus Christ who is the one and only Word of God.

In his book The Mediation of Christ, T. F. Torrance explains this Barthian concept with a helpful explanation that “the real text of New Testament revelation is the humanity of Jesus.” The New Testament is not the revelation of God in itself, because it contains Gospels and Epistles that tell us about Jesus Christ. I believe it is easy to understand that the New Testament is a book about a person, and that the Bible doesn't point to itself but instead it points to Jesus. However, several people have been confused how the Old Testament is a witness to Jesus, when it is difficult at times to see Jesus in the Old Testament without the illumination of the New Testament, and because the incarnation had not yet happened. 

Karl Barth said that there is no such thing as an unincarnate Word of God, so it is wrong to believe that the Word of God ever existed apart from the humanity of Jesus. There was a specific time when the Word of God became flesh—at the Virgin Birth—but that does not mean that the Word of God ever existed without flesh. Karl Barth said there is no such thing as a logos asarkos (or unincarnate Word of God), because even before the incarnation happened, the Word of God has always been a Word of God that will be incarnated (logos incarnandus). So even the Old Testament is a human witness to the humanity of Jesus who is the one and only revelation of the Word of God. 

Barth's concept of logos incarnandus is difficult to explain, so I really appreciated T. F. Torrance's simple explanation of it as follows:

. . . the real text of the New Testament revelation is the humanity of Jesus. As we read the Old Testament and read the New Testament and listen to the Word of God, the real text is not the documents of the Pentateuch, the Psalms or the Prophets of the documents of the Gospels and the Epistles, but in and through them all the Word of God struggling with rebellious human existence in Israel on the way to becoming incarnate, and then that Word translated into the flesh and blood and mind and life of a human being in Jesus, in whom we have both the Word of God become man and the perfect response of man to God offered on our behalf. As the real text of God's Word addressed to us, Jesus is also the real text of our address to God. We have no speech or language with which to address God but the speech and language called Jesus Christ. In him our humanity, our human understanding, our human word are taken up, purified and sanctified, and addressed to God the Father for us as our very own—and that is the word of man with which God is well pleased. [1]

Sources:

1. Thomas Forsyth Torrance, The Mediation of Christ, (Helmers & Howard Publishers; Revised edition: 1992), pp. 78-9

2. Book in the background of the header image (source: wikipedia).