The 144,000 is brought up early in the Revelation of Jesus Christ. The sealed in their foreheads. First mention is in the breaking of the seals of the book of God by Jesus Christ. This is important because when God's book is opened in our life, everything changes.
People get confused with the natural and the spiritual when looking at the book of Revelation. If we make Isreal natural, we miss the intent of the spiritual.
Revelation 7:4 And I heard the number of them which were sealed: and there were sealed an hundred and forty and four thousand of all the tribes of the children of Israel.
The 144,000 is not a number of people, it is a symbol of perfect government, it is a symbol of a government order or body of people who follow only Jesus Christ.
Isreal is not nature Isreal it is spiritual Isreal, of which all the children of the new birth in Jesus Christ are a part of. You are spiritual Isreal.
"The Bible says there wrestled a man with Jacob all night long. And toward the breaking of the day, when he prevailed not, the man touched the hollow of Jacob’s thigh and Jacob became absolutely helpless and could walk no longer in his own strength. And then the picture changes. No longer is the angel of the Lord wrestling with Jacob, but now Jacob is wrestling with the angel of the Lord! And he takes a fresh hold upon the angel of the Lord, and the angel of the Lord said, Let me go, for the day breaketh. The angel really didn’t want Jacob to let go, he was only testing Jacob to see how hard Jacob could hang on. And Jacob takes a fresh grip, and says, I will not let you go until I get the blessing! And the angel of the Lord says, What is your name? He says, Jacob, — schemer, grasper, supplanter. And the angel says, No, thou shalt no longer be called Jacob, but Israel, Prince of God! For as a prince hast thou power with God and men, for thou hast prevailed. No longer Jacob, schemer, grasper, supplanter, but Israel, Prince of God. And as such Jacob was only the type of all those in every generation that God calls by His Spirit, out of the world, to change their nature from the nature of schemer, grasper, supplanter, that is, fleshly dependency and effort, to a prince of God with power. Then He gives them a new name to fit their new nature! Therefore, Jacob was the first Israel, for he was the first called out of the world that God might change his name and his nature."
Much more in the link:
“Out of Jacob came twelve sons and they were mighty ones, God’s Israel for that generation. Out of them came twelve tribes, and they were God’s Israel for their generation. Then, finally, out of the twelve tribes came Jesus, and while Jesus was in the world, He was God’s Israel, God’s Prince. Then out of Jesus came a generation of enChristed Israel and they were God’s Israel, God’s mighty ones, for their generation. Then over the last 2,000 years have come generation after generation of enChristed Israel. Each out of the previous generation, and they were God’s Israel for their generation and now, we who have been called and chosen by the Spirit of God out of the masses of the world and religious Babylon, that God might deal with us and change our nature, that he might change our name — we are God’s Israel for our generation!"