And the Word became flesh and lived among us, and we have seen his glory, the glory as of a father’s only son, full of grace and truth.
Suffice it to say that things get much more controversial and significant when John gets to that line about the Word becoming flesh. That was the big claim that made the philosophers hesitate when it came to this new religion. A divine Word carrying out the creative work of God is one thing; that Word becoming flesh, becoming human and living--and being crucified!--among us is another matter. It seemed impossible, not to mention absurd, that the creative power of God should be humbled to earthly existence like that. And yet without that claim, I don't know what Christianity would have become--maybe nothing more than a disappointed Messianic cult that died out as its hopes of vindication within history gradually failed.
Through centuries, and still today, we have to continually hold to this claim against all kinds of skepticism. There were arguments about how exactly the Word and human flesh were connected: was Jesus just an appearance of humanity, or was the Word inside his body, like an astronaut in a space suit? Does it mean that he became the Son of God at some point in his life, such as at his baptism? Or is it really just a way of saying Jesus was especially enlightened and knowledgeable about the Word of God?
The church answered those questions over the years: no, Jesus was not merely apparently human but was really fully human; no, the divine Word wasn't inside him like a parasite in a host, but was truly one with his human flesh; no, Jesus didn't suddenly turn into the Son of God and he wasn't just an especially enlightened or knowing individual. We come back over and over again to the insistence that the eternal, perfect, immortal Word of God was made human flesh and connected God and humanity forever. This insistence changes everything. We aren't just spirits trapped in human bodies. We aren't supposed to be indifferent to our own bodies or the bodies of others. Our frail, mortal, temporary human flesh became the dwelling of God the Word--the Greek word we hear as "lived among us" could be more literally translated as "pitched his tent among us"--and so even our weakness and our suffering and our hindrances are taken up into the absolute holiness of God.
For more on this topic, you might want to take a look at a central piece of the argument over the meaning of these words, a treatise by Athanasius of Alexandria called On the Incarnation of the Word.