What does the Bible actually say about the 144,000?
At Revelation 7:2-8:
And I saw another angel ascending from the rising of the sun, having the seal of the living God; and he cried out with a loud voice to the four angels to whom it was granted to harm the earth and the sea, saying, "Do not harm the earth or the sea or the trees until we have sealed the bond-servants of our God on their foreheads."
And I heard the number of those who were sealed, one hundred and forty-four thousand sealed from every tribe of the sons of Israel: from the tribe of Judah, twelve thousand were sealed, from the tribe of Reuben twelve thousand, from the tribe of Gad twelve thousand, from the tribe of Asher twelve thousand, from the tribe of Naphtali twelve thousand, from the tribe of Manasseh twelve thousand, from the tribe of Simeon twelve thousand, from the tribe of Levi twelve thousand, from the tribe of Issachar twelve thousand, from the tribe of Zebulun twelve thousand, from the tribe of Joseph twelve thousand, from the tribe of Benjamin, twelve thousand were sealed.
Revelation 14:1-5:
Then I looked, and behold, the Lamb was standing on Mount Zion, and with Him one hundred and forty-four thousand, having His name and the name of His Father written on their foreheads. And I heard a voice from heaven, like the sound of many waters and like the sound of loud thunder, and the voice which I heard was like the sound of harpists playing on their harps. And they sang a new song before the throne and before the four living creatures and the elders; and no one could learn the song except the one hundred and forty-four thousand who had been purchased from the earth. These are the ones who have not been defiled with women, for they have kept themselves chaste. These are the ones who follow the Lamb wherever He goes. These have been purchased from among men as first fruits to God and to the Lamb. And no lie was found in their mouth; they are blameless.
Several things about them are conspicuously absent. Nowhere does it say that they are the only ones going to Heaven. Or that they have some special position of authority among Christians. Nothing is said about 1935. Nothing is said of people being chosen for this group and later being replaced if they are found unfaithful. Nothing is said of these being the only Christians throughout history to be in the new covenant or to partake of the Lord's Supper. All of this, and much more, is Watchtower fiction constructed for the primary purpose of establishing their own authority.
In fact, it is apparent that ALL members of this class are alive on earth at the very end time, and not spread out through history, since they are ALL sealed before the judgments of God issue upon the earth, and they are ALL present to stand with the Lamb on Mt. Zion upon his return.
It is also apparent that they are Jewish, since they are spoken of as coming from the twelve tribes of Israel.
Some dispensationalists argue that these are a group of Jews who arise during the seven-year Tribulation period as evangelists to bring the message of salvation to the world. I'm not sure whether that is correct or not, but it makes a whole lot more sense than anything the Watchtower teaches on the subject, and doesn't require nearly as much embellishment of what the scripture actually says.
Now, you can still argue as does the Watchtower if you want. You can assert that the "Lamb", "Mt. Zion", "twelve tribes of Israel" and all the other features mentioned in this prophecy are symbolic. And I'd agree on some of it. The Lamb spoken of is clearly Jesus, not a literal lamb. But if all of the features surrounding this prophecy are figurative in nature, what is the basis for insisting that the number 144,000 is a literal number?