Though the Watchtower teaches such hearsay, the Bible does not.
Nothing in the passage leads to interpreting the 144,000 as anything but a literal number of Jewish individuals; specifically 12,000 chosen from the tribes of the children of Israel, according to verses 5–8.
These are not Gentiles or Jehovah’s Witnesses. The text clearly states and lists that these are 144,000 from the tribes of Israel. 12,000 from each tribe are sealed, meaning they have the special protection from God. They are kept safe from Divine judgments and from the Antichrist during the the Tribulation period because God has a mission for them to accomplish.
The Bible teaches that God selects 144,000 faithful Christians to be resurrected to life in heaven.
These 144,000 are not safe or exempt from Divine judgement. They must, in fact, continue to maintain a Christian standard of faith and conduct in order not to be disqualified from receiving their heavenly inheritance. (Philippians 3:12-14) (Ephesians 5:5)
The 12 tribes of Israel listed in Revelation chapter 7 cannot be the 12 tribes of natural Israel listed at Numbers chapter 1. The listings between the two do not match.
In Revelation it mentions the tribe of Levi, but the Levites were set aside for service in connection with the temple and were not reckoned as or listed as one of the 12 tribes in the book of Numbers. (Numbers 1:47)
The tribe of Joseph is mentioned in Revelation. There never was a tribe of Joseph and it is not included in the list of the 12 tribes of natural Israel in the book of Numbers.
Revelation 7:4 says that people would be sealed out of every tribe of the sons of Israel, but the tribes of Dan and Ephraim are not mentioned and are not included on the list.
And so, the 12 tribes of Israel listed in Revelation are not natural Israel. It is spiritual Israel, the Israel of God. (Galatians 6:16) (Romans 2:29) (Romans 9:6)
The natural Jews and Jewish proselytes were given the first opportunity to be chosen to make up the 144,000 of spiritual Israel, but only a minority of that nation responded. The majority rejected the Lamb, Jesus Christ which is why Jesus told them that the kingdom of God would be taken from them and given to a nation producing its fruits. (Matthew 21:43)
Jehovah therefore extended the invitation to the Gentiles which meant now non-Jews could be sealed with God's spirit and become part of the congregation of anointed Christians who make up spiritual Israel, the Israel of God. (1 Peter 1:29) (Ephesians 3:5-6)