Babel was a place of unity, but it was not unity around a valid cause. Instead, it was a unity around an egotistical, arrogant cause: to make a name for themselves(v. 4). The men of the city purposed to build a tower whose top was in the heavens. This signified their desire to be equal with God in fame and renown. While unity can be a powerful force for good, if the motive and purpose are pure, unity around a negative or impure purpose is equally powerful, but negative. People have amazing abilities and gifts, some of which are used for the Lord, and some which are used for negative or selfish ends.
While some sinful pursuits are successful, there are cases where God intervenes in circumstances and changes history in order to effect his purpose. There are those purposes which God knows are so contrary to His purpose or plan, that He stops them in their tracks. For whatever, reason, this was one of those purposes. Perhaps what God did had a higher purpose. With their languages confounded, the people felt the need to scatter, or perhaps the necessity to scatter. God’s purpose to cover the earth was fulfilled through the confounding of the languages. Without this event, the people may have stayed in one general area of the earth. Overcrowding would have occured, and parts of the earth would not have been inhabited.
God’s purposes often confound man’s plans, but that is okay. God knows best.