The 144,000 in Revelation 7:4 are from the 12 tribes of Israel
Do not harm the earth, the sea, or the trees until we have put a seal on the foreheads of the servants of our God.” 4And I heard the number who were sealed. One hundred and forty-four thousand sealed from all the tribes of the children of Israel. –Revelation 7:3-4 (GFS)
This 144,000 number does not represent the total number of people who will make it into heaven. That is a belief held by Jehovah’s Witnesses. As of research done thru 2015, there are 2.3 professing Christians in the world today. That represents bout 31.2% of the world’s population. This information was obtained thru the Pew Research Center.
You would imagine that even if most of those professing to be believers was actually less, there would still have to be at least 144,00 that would qualify as Christians. Beyond that there isn’t much said regarding this unique number except that they come from the 12 tribes of Israel. This reference to the 12 tribes is an interesting one as the names of the tribes of Israel here is different than the list found in Genesis 49 and Numbers 1-3. The list of names is different. Here we have a list including Levi and Joseph and omitting Dan and Ephraim.
In the Old Testament while Levi was considered a tribe, it was not considered one of the 12 tribes of Israel. The reason is that the tribe of Levi had no inheritance among the people.
But unto the tribe of Levi Moses gave no inheritance; the Lord God of Israel was their inheritance as he declared to them. –Joshua 13:33 (GFS)
There is much speculation as to why the names are different but the Bible is silent on the matter. But there is an additional reference to 144,000 found in Revelation 14. The Bible does not state that this second reference is speaking about the 144,00 in Revelation 7.
And I looked, and behold a Lamb stood on Mount Zion, and with Him 144,000, having His Father’s name written on their foreheads. 2 And I heard a voice from heaven as the voice of many waters, and as the voice of loud thunder. And I heard the sound of harpists playing their harps. 3 And they sang a new song before the throne and before the four beasts, and the elders and no man could learn the song except the 144,000 who were redeemed from the earth. 4 These are the ones who were not defiled with women for they are virgins. These are the ones who follow the Lamb wherever he goes. These were redeemed from humanity as firstfruits to God and to the Lamb. –Revelation 14:1 (GFS)
One question that does come to mind however is if the 144,000 are saved and get a special mark, are there additional people who get saved and do they also get this mark? The rapture hasn’t happened at this point in the chronology of Revelation (it happens between Revelation 11:15 and Revelation 14) so it is clear that people can still be saved. What these guys, and I mean young men, not women, in this group do throughout the book of Revelation is unclear. Some say they are supernatural evangelists. If they are the same 144,000 as the group in Revelation 14 then they were never married as they were not defiled with women and they were virgins.
Those are the only two references to 144,000 in the book of Revelation. You can go online, read books, look at videos and get lots of opinions regarding the identity of this special group, and their purpose. But the Bible is silent on the matter.