The first part of John 1:10 says, speaking of the Logos: He was in the world.
These short words, only four of them in the original Greek, express the fundamentally real and concrete nature of Christian faith. In other words, belief in the Christian message is belief about something in the real world of history, about something that actually took place. The Logos, the very same Logos which created the world in the beginning and which is God, came into this world and lived among human beings. He was in the world, really, the same way John and Paul and Peter and the rest of them were in the world. He walked about Palestine, during a specific identifiable period of history.
In this way Christian faith is to be distinguished sharply from ancient mythologies which tell stories about "events" that took place in some nondescript no-time. The Bible in general doesn't read in this way, and it is typically people who have never read the Bible before in any detail who think of it as stories and myths, or else people who are intent not believe in what the Church has traditionally taught. On the contrary, the Bible attempts to speak about reality, about existence, about what is really there in everything that it says. Christian faith is not mythological or a belief in "parables," like Fox Mulder from The X-Files so often describes it.
An important consequence of this is that Christian faith is not primarily about sentiments or feelings or the "interior" world of the subjective mind. So many people -- especially here in Romanian culture -- think of the Christian religion and its practices in these interior terms. Going to the liturgy is worthwhile because the experience is so profound, because it gives an inner peace, because it calms your spirit, and so on. All of that is not bad in itself, but neither is it the whole story. It does us little good to feel fine on the inside but actually to be in danger. Imagine a person who is soundly sleeping or else enjoying himself on a ship that, unbeknownst to him, is slowly sinking. His state is hardly a good one just because he feels fine about himself and about his estate; on the contrary, his state is that much more miserable because he's not aware of just how much danger he is in!
The more important factor, according to the Christian religion, is to be in the truth, regardless of how you feel. This is because He was in the world; because Christian belief is primarily about the truth, and not about custom or feeling or sentiment or anything else of the sort. It is better to be in the truth, really to be reconciled to God and in his grace, than to feel good about yourself despite really being separated from God's favor because of unforgiven sin.
These, then, are some remarks on the significance of that verse: He was in the world. The important thing to remember is that Christianity is primarily a religion of the truth, of reality, and not of mythology or of empty religious sentiment without any greater reference to the actual state of things.