Is the number 144,000–used when speaking of the people that will come to Heaven–a specific number, or a number that symbolizes many people?
The number is clearly symbolic, as are other numbers in apocalyptic literature like Revelation. 144,000 is a multiple of 12, as in the twelve tribes or the twelve apostles. As such it symbolizes the whole people of God, however many actual numbers of them there may be.
—Ben Witherington III