Language is essential to our identity as human beings. Language shapes our thoughts, our culture, and our understanding of the world. There are thousands of different languages in the world, and this hinders our ability to communicate with others and often leads to conflict.
In this passage, humanity is united, with one language. This may seem like a good thing at first glance, but humanity was united in rebellion against God. The people's desire to stay together in one city was in disobedience to God's command for humanity to fill the earth (Genesis 1:28); by building a tower "to make a name for ourselves", the people were trying to rule heaven and earth without God. God thwarted their plans by mixing up their languages.
At the Tower of Babel, people were united in defiance against God. At Pentecost, God began to re-unite people with each other, and with him.
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