14The word became flesh and dwelt among us. We have seen his glory, the glory of the only begotten (or the one and only) from the Father, full of grace and truth.So where was Jesus before he "became flesh"? First, let's see how the context can help us. A few lines up we see this:John 1:14
1In the beginning was the Word, and the Word was with God, and the Word was God. 2He was with God in the beginning. 3Through him all things were made; without him nothing was made that has been made. ... 9The true light that gives light to every man was coming into the world.So the first answer to "Where was Jesus before he was born?" is this: He was with God, and he was God. Verse 9, which says he was "coming into the world," implies that he was not in the world immediately before that.John 1:1-3,9
Back in verse 14, we read that the word "became flesh," which says that, at least just before this, the word was not a physical human being.
So he was not in this world, and because he wasn't a physical being, perhaps he didn't have a location, didn't have spatial coordinates.
Those are some clues from John chapter 1; how about other parts of the Bible?
Later on in John's gospel, Jesus talks about the glory he had with the Father before the world began. And later in the New Testament, the Apostle Paul writes about how Jesus was "in the form of God" (the NIV renders this "...being in very nature God" -- being equal to God in his essence I guess), which confirms the idea of not being a physical being, but doesn't say much about where he was or what he was doing in earlier centuries.
Some time ago, I heard the theory that "the angel of the Lord", who appears quite a lot in the Old Testament, is actually Jesus Christ before his incarnation. I'm not sure that I could prove it, but the theory seems at least plausible to me. Take a look for example in Genesis 22, when Abraham is about to sacrifice his son:
11But the angel of the Lord called out to him from heaven, "Abraham! Abraham!"Notice how the angel says "I know that you fear God" but immediately afterward says "not withheld your son... from me". Abraham was going to make a sacrifice to God, which the angel took as being for himself -- that is, the angel speaks as though he were God himself... and yet also speaks of God in the third person. Which sounds familiar: "The word was with God and the word was God."
"Here I am," he replied.
12"Do not lay a hand on the boy," he said. "Do not do anything to him. Now I know that you fear God, because you have not withheld your son, your only son, from me."Genesis 22:11-12
If that's true, then Jesus might have been coming to earth and appearing to people occasionally -- a dozen times or more -- in Old Testament times.
So what does all this mean? Well, what it means to me is that the whole plan, where Jesus becomes flesh and comes into the world, gives life to us who are dying, then sacrifices himself for us -- this plan was never a surprise to Jesus; he knew it from the time the world was created.
What a great love he had for us -- has for us -- he had all that time to think about it; he visited the earth time and again, saw our depravity, our poverty, and still came to live it with us. And die for us.