I love this passage.
There's a play on the word "Word".
Notice that Bibles (other than the Jehovah Witness translation) have capitalized the "W".
I believe that there are three simultaneous meanings to this "Word".
In Genesis, a promise is made to Adam and Eve that there will come a deliverer. God gives them His "Word" on this. God's "Word" is His promise.
Jesus is the fulfillment of that promise. That makes Him the Word.
The Bible is God's word. The Bible describes Jesus relentlessly, figuratively (prophecy) and literally.
Another more modern usage in our culture is "Word!". When this is said it indicates that the speaker recognizes the truth of the statement just uttered.
So the Word in question can be simultaneously: God's Promise, Jesus (the promise fulfilled) and the Bible (Jesus described).
We do not have a physical description of Jesus. We have a "word" picture of Jesus. This appears to be intentional. A thousand words are worth one picture.
And the Bible is an elaboration on the original promise made.
