Immanuel-Christ-Jesus brought the Kingdom of Heaven to earth; and made it available to who-so-ever-will. From the beginning of this earth-age, our Creator has had Saints on the face of the earth. For almost 2,000 yrs. people have been guessing, and pronouncing who the Saints are, in their own opinion, Vs. looking to the LORD.
"An hundred and forty and four thousand" is mention in The Revelation of Jesus Christ, Chap. 7; and again in Chap.14. One must be Spiritual-minded, and ask for assistance from GOD's-Spirit, for Understanding. Non-believers and Hypocrites don't stand any chance of understanding the Word, and are Blind.
The 144,000 represent Twelve-Tribes of the House of Israel: Dan, and Ephraim are the only two that are omitted. The "Key of David" is found in Gen.35:22, Num.1, 1Chron.2, and Gen.49. The Truth is anti-deception, and will set people free.
This group of 144,000 are descendants on the EARTH. The Sealing inside their brains = they know the Truth, and are the counter-balance of deception: they actively "stand" against, deception! Sealed, and set apart, for GOD's purpose.