I found this on a chat board at the following link:
The number 84 is highlighted more than once in the Bible. First, it is found during the famine of Jacob's day. Jacob and his house went into Egypt after two years of a seven year famine. Incidentally, 7 years equals 84 months. Again, in the days of Jeremiah, in the 23rd year of Jeremiah receiving the word of God, God declared a 70 year tribulation period for the nation of Judah. Incidentally, this was four years after it had begun; 70 years equals 840 months. Comparatively, Genesis 7:4 declares that in 7 days a flood of waters would come upon the world. In 2 Peter 3:8, in speaking of his Final Judgment and how it relates to the flood, God declares a day as a thousand years and a thousand years as a day. Effectively, declaring in Genesis 7:4 that in 7000 years his final judgment would come. Incidentally, 7000 years equals 84000 months.