The 144,000 are not literal Jews from the 12 tribes because:
In the Old Testament during King Hezekiah’s reign, the Northern kingdom, which is where the 10 tribes dwelt (often called the kingdom of Israel), was conquered by the Assyrians. And the people were carried away to Assyria. There they were inter-married, enslaved, absorbed and they lost their distinct identity as a people.
The Jews were the Southern kingdom of Judah. In the Southern kingdom, there were the tribes of Judah, Benjamin and Levi. Levi wasn’t really counted as one of the tribes because they were the Priests. The people of Judah, Benjamin and Levi were carried away captive to Babylon. And they came back after 70 years, but the 10 Northern kingdoms never came back. So, when we talk about Jews, we’re talking about Judah. We’re not talking about the other 10 tribes.
The 144,000 are not literal Jews but figurative Israelites, spiritual Israel, and the Christian church (Rom. 2:28, 29; 9:6, 7; Gal. 3:28, 29; 6:16; Gal. 4:28; 1 Peter 1:1; Phil. 3:3).
Twelve is considered by many Bible students a significant number in the Bible, doubtless because there were 12 tribes in Israel (Ex. 24:4; 28:21; Lev. 24:5; 17:2; Matt. 10:1; Rev. 12:1; 22:2). The twelve fold repetition of the number 12,000 (Rev. 7:5–8) may suggest that the principal aim of this passage is not to disclose the precise number of the sealed but to show the distribution of the sealed among the tribes of spiritual Israel.
The 144,000 are those who are “able to stand” through the terrible events portrayed in Rev. 6:17. They have the “seal of the living God” (Rev. 7:2) and are protected in the time of universal destruction, as were those who possessed the mark in Ezekiel’s vision (Eze. 9:6). They are approved of Heaven, for John later sees them with the Lamb on Mt. Zion (Rev. 14:1). They are declared to be without guile and without fault (Rev. 14:5). John hears them singing a song that “no man could learn” (Rev. 14:3). They are designated as “first-fruits unto God and to the Lamb” (Rev. 14:4).
In His service,