Revelation 14:1 (ESV)

1 Then I looked, and behold, on Mount Zion stood the Lamb, and with him 144,000 who had his name and his Father’s name written on their foreheads.

The number 144,000 is the second number John mentions within two verses; in Revelation 13:18 he had said that the number of a man was 666. This Lamb attracts an incredibly larger number than the one typifying humanity. That in itself signifies that the Lamb is infinitely superior to man.

Furthermore, we had already met the number 144,000 in Revelation 7:4. 144 is the product of multiplying 12 by itself. The number 12 is highly significant in Scripture, being the number of the sons God gave to the patriarch Jacob, and thus the number of the tribes of Israel. The number 12, then, represents all Israel. The Lord Jesus Christ appointed 12 disciples to serve as the foundation of his New Testament church (see Mark 3:13–19; Ephesians 2:20). We are to notice, though, that the number John hears is not 24(000), that is, 12 plus 12, Old Testament Israel plus New Testament church. The number is 144(000), that is, 12 x 12. The point of the multiplication of 12 by itself is to give expression to the Lord's fulfilling his promise to Abram that his descendants would be as many as the stars of heaven (Genesis 15:5). The addition of the thousands to the number points in the same direction. 1000 is 10 multiplied by itself not 2 but 3 times! Such is the generosity of the Lord’s mercy; he is not stingy so as to save only a few from Satan’s bondage. The total number 144,000 is symbolic; it does not mean that precisely 144,000 individuals will be saved (see also Revelation 7:9). The number points to the totality of the elect of God from every tribe, language, and race (recall again Psalm 87:1–7).

This vision is not meant to conjure up in our minds the innumerable host of the redeemed who enter the New Jerusalem on the Last Day (though of course these people would). What John sees here are the chosen of God scattered across the earth throughout the ages as they gather where the gospel of the Lamb is proclaimed.