Who are the 144,000?

Of course like many things in Revelation depending on the school of belief, everything is looked upon differently.

From what I understand the preterist (most everything happened long ago) tends to think of them as literal Israelites that were spared in the destruction of Jerusalem who had faith in Christ. The futurist (everything has not happened yet) also tends to take it as literally Jewish people who will be spared in some future period. The symbolic view usually assigns them as a symbol of the total church, including both Jew and Israel. The view I am most persuaded by is the historical which assigns the meaning to around the time after the overthrow of heathenism in the Roman empire.

Shortly after Constantine the church became filled with unbelievers naturally as it became the Roman thing to do. While the bulk of its external members would become in profession and external baptism the Christian Israel or Church, God’s true Israel or Church would be but a small election out of it.

The sealing of God, of the elect, seems to take a ironic predictive vision of the corruption that the Roman Church begun to introduce at this time. At this time the external rite of baptism transformed into a somewhat superstitious sealing of the elect for salvation. In contrast to this the vision of the 144,000 indicates God's true sealing and preserving of his elect in the onrush of false believers into his church external.

One author that really captures both the history and the predictive element of the Apocalypse is Elliot. He shows that in every detail, the sealing of God is in a negative and allusive contrast to the superstition that now became the standard way to pretend to seal the elect of Rome, which the apocalypse shows is opposed to God's actual sealing. Under the historicist view the 144,000 represents the small elect population of Jew and Gentile among the wide and populous Roman Church after Constantine. A theologian that most perfectly representing one of these elect and coincidentally was facilitated with the doctrine of election around the same time! is St. Augustine.

Here is Elliot showing the allusive contrast and parallel between the established superstitious rite of baptism and sealing at the time verses John's contrasted vision of God's true sealing of his church:

And now it is needful that I draw the reader’s attention to the parallel, or rather contrast in the way of parallel, which, point by point, meets the eye between this historical picture of the general professing Church catholic of the æra of Constantine, after becoming sole Emperor, and his successors in the 4th century, (specially in respect of the initiation of its members,) and that of the 144,000, God’s election of grace chosen out from them, as sketched to us in the Apocalyptic vision? In the ecclesiastical phraseology of the times,—a phraseology continued, it is to be observed, from Constantine’s time downwards,—the former were the elect, holy, and faithful. In the divinely inspired language of the Apocalypse these same titles elect, holy, faithful are attached to the latter, and to them distinctively and alone.2—The former, we read, claimed to have been marked with what they called the Lord’s seal and mark upon the forehead; yea, and often actually bore there a visible mark in sign of it: it was the seal of water-baptism, impressed on them by the officiating presbyter, and perfected with the chrism of the confirming Bishop.1 The latter are here represented as marked with God’s true seal on the forehead; even the seal of the Holy Spirit’s baptism, and as applied by Christ himself.—The former, looking to the east at the time of baptism, were supposed to receive from it, (and perhaps through angelic ministration on the waters of the font,) both life from the death of sin, and spiritual illumination as from Christ the Sun of righteousness. (HORÆ APOCALYPTICÆ, Vol 1, P282, Elliot)

Even the angel in John's vision coming from the est to seal the elect matches the rite of baptism applied superstitiously in the Roman Empire, where the receipient looked to the east and received the sign of the cross on his forehead claiming external sealing by the power fo the Bishop.

Here are some of the ways to interpret the 144,000.

1. Some of them are from the first century Christians and the remnants are from some faithful members of Jehovah's Witnesses.
2. They are the chosen people at the last days who will proclaim the last Gospel to the world.
3. They are literally from the 12 tribes of Israel. (I endorse this view)

Let's take 144,000 literally that they are from the 12 tribes of Israel.

One important thing to know is that Jews today living in Israel are from one of the 12 tribes of Israel. They are the descendants of Judah, the fourth son of Jacob(Israel). Even during the time of Jesus, there were only Jews, not the whole Israelite. We don't know where are the other remaining tribes of Israel. Ten tribes of Israel are lost till today. If we take 144,000 literally, then it must be from the 12 tribes of Israel only. The Gospel was preached only to the Jews and then to Gentiles. I believe that God wants to save the whole 12 tribes of Israel. This may be the reason why Rev 7 list down the 12 tribes. Even though 10 tribes are lost, I believe that God still knows where they are and God has a complete list of all the descendants of Jacob. There are many theories and studies on who are the lost tribes of Israel but God knows it better. The descendants of Jacob, especially the Jews will believe in Jesus at the last days through the two witnesses, the last prophets who will convince the nation of Israel that Jesus is the Christ. These two witnesses will preach in Jerusalem and ultimately will be killed by the Antichrist but God will raise them after 3 days(Rev 11).

Why 144,000? There can be two possible views on this.

1. Total number of Israelites in Heaven: We don't know how many Jews believed the Gospel till today. We don't know whether the number 12,000 allotted for Jews is already completed or not. We also don't know how many from the lost tribes have already believed in Jesus. But at the last day, all complete 12 tribes will believe Jesus Christ, whether they are lost or not and their will be exactly 144,000 people in Heaven from the descendants of Jacob.
2. The elected evangelist at the last days: God will chose 144,000 people from the descendants of Jacob in the last days and they will preach the Gospel to all the nations.