The 144,000, again symbolic, represent all believers. 12 represents the authority and perfection of God’s kingdom. 12 x 12 x 1000 (a huge uncountable number) represents the whole kingdom of God, those faithful to Jesus Christ

The first tribe listed is Judah. Jesus is the lion of Judah, the firstborn over all creation.

The two tribes missing are Ephraim and Dan. The message here is that, these two tribes were where Jereboam set up the calf idols in the northern kingdom, so his people didn’t need to go to Jerusalem to worship God. Those excluded from the 144,000 are those who do not belong to Jesus, but have given themselves over to their own beliefs and idols.