144,000 is a symbol, meaning that the numbers are beyond counting or unfathomable to man (Rev. 1:1; 2:20; 22:6). This denotes how Israel returned from the Babylonian captivity to inherit the land (Ezek. 48). This also alludes to us, the Church, who are the inheritors (Rom. 11:1-36; Rev.12). In Rev Chapter 7, it is set in twelve series of 12,000. Twelve, like most numbers in Revelation, is not an actual number nor is 12,000 or 144,000; rather it refers to “fullness.” Twelve is also found, in various Jewish sects and in the Dead Sea Scrolls, to mean “the people of God.” Then the “12” is magnified as to 12 multiplied by 12 to mean complete fullness or God’s bountiful provisions and blessings. This is a symbolic Jewish metaphor for being “servants of God,” just as the key phrase previous to this symbolizes. This also means that He is the Provider. The debate over the numbers centers on whether they represent the entirety of saved souls or just those who just are “restored” Jews. Nonetheless, the term “servants of our God” makes it more understandable (Ezek. 9; Matt. 10:30; Rev. 9:4; 14:1-5; 21:8; 22:15).
Remember, the context is also about worship and church leadership. Jesus is the ONE who is qualified and able to judge and, by his grace, to give us a reprieve. It is amazing of all the convoluted theories on this number that ignore Jewish customs, apocalyptic metaphors, and of course, the context and Old Testament that tell us the meaning. Many commentators see this passage as just pertaining to actual Jewish tribes or a group of Jewish believers who convert during the period of tribulation.
We are not told exactly who and what these 144,000 are. Possibly, it is because it is not important, as the reason and purpose of pointing to Christ and showing us opportunities to get our priorities in line with His are far greater. We can either honor His name by living lives worthy to be in Him, or we can reject His offer of salvation and reconciliation and do as we want; and we can “want” ourselves all the way from judgment to hell. The bottom line meaning is that God keeps His promises to individuals and to people groups, as He here confirms.
The point of this passage tells us that God is at work even when all seems lost¾and then it gets even worse! God is still there, even in tribulations, no matter how short or great His love and grace are carrying us through it! The purpose that John has in mind, and what God calls us to in the context of this passage, is the obvious: Beware! Judgment is coming! And now, here is some grace. Here is a quiet time so you can assess where your priorities and direction in life will be, but there is not much time.
For more see http://biblicaleschatology.org/rev-7/