There seems to be some controversy over my brief words about Christmas yesterday. The topic of debate is the question as old as Christianity itself: "Who is Jesus?" Is he God? Is he human? Is he, perhaps, half-god and half-human like people at the time said about Hercules?
Fortunately for us, we don't need to worry about this issue. In 451, at the Council of Chalcedon, all the bishops in the world came together to settle the debate once and for all. No one was excluded because of their beliefs. Over a series of sixteen sessions, they discussed the nature of Christ (and many others) at length.
At the end, the Bishops decide to make full use of a helpful suggestion by Pope Leo I, now known as Saint Leo the Great. They solemnly declared that Jesus is both fully God and fully human. In other words, Jesus has two natures in one person.
This was an exercise of extraordinary magisterium, the highest teaching power of the church. To put it in layman's terms, this teaching is infallible. The church recognized that this was one of the rare circumstances in which they could invoke infallibility, and because it was an incredibly important issue, they decided to do so. That was the purpose of the council: to get an infallible definition of the nature of Jesus, which would decide the matter for all time.
Saying Jesus is fully God and fully human is not only the correct answer to the question of Jesus' nature, but it's also the best one. The problem with saying "Jesus is 100% God and 0% human" is that it means Jesus didn't really die for our sins; he just pretended to die. The problem with saying "Jesus is 0% God and 100% human", which is a very popular idea today, is that it completely erases Jesus' authority and power to forgive sins and give life. There are more problems than these; I'm just giving examples to show that it's difficult to build a theology which tries to balance God and human in Jesus. More often than not, you end up overemphasizing one nature, and the other one gets diminished. That's why the correct answer is not "either/or"; it's a "both/and". By saying "Jesus is fully God and fully human", we are not limiting either of the two natures of Jesus.
Of course, when Protestantism and other Christian denominations were invented about a thousand years later, many of them decided to re-open the question of Jesus' nature. So now beliefs on this topic are all over the board. But for Catholics, at least, that question has been dead for a really long time. We say he's both God and human, and there's nothing which could make this answer change. Beliefs as to what this means and how this affects our religion, yes, those can change. But the solemn definition of Jesus as both God and man cannot.