What does it mean to be sealed?

I'm not sure exactly but it seems to be some sort of honor as far as I can tell.  I think this is another set of verses that confirms my belief that we are not all treated equally in Heaven.  Take a look and then as usual I will give my take. 

Revelation 7:4-12(NKJV)

And I heard the number of those who were sealed. One hundred and forty-four thousand of all the tribes of the children of Israel were sealed:

    of the tribe of Judah twelve thousand were sealed;      of the tribe of Reuben twelve thousand were sealed;     of the tribe of Gad twelve thousand were sealed;

    of the tribe of Asher twelve thousand were sealed;     of the tribe of Naphtali twelve thousand were sealed;     of the tribe of Manasseh twelve thousand were sealed;

    of the tribe of Simeon twelve thousand were sealed;     of the tribe of Levi twelve thousand were sealed;     of the tribe of Issachar twelve thousand were sealed;

    of the tribe of Zebulun twelve thousand were sealed;     of the tribe of Joseph twelve thousand were sealed;      of the tribe of Benjamin twelve thousand were sealed.

After these things I looked, and behold, a great multitude which no one could number, of all nations, tribes, peoples, and tongues, standing before the throne and before the Lamb, clothed with white robes, with palm branches in their hands, 

and crying out with a loud voice, saying, “Salvation belongs to our God who sits on the throne, and to the Lamb!” 

All the angels stood around the throne and the elders and the four living creatures, and fell on their faces before the throne and worshiped God, 

saying:      “Amen! Blessing and glory and wisdom,     Thanksgiving and honor and power and might,     Be to our God forever and ever.     Amen.”

First let me set the stage.  John is being shown visions of Heaven by Jesus and is told to record them.  This results in the book of Revelation.  In Heaven you see God and Jesus.  Then you have the 144,000 who are "sealed" which seems to be some type of honor.  I then highlighted in green the next group that is there in Heaven with them.  "A great multitude".  Who are the great multitude? 

Revelation 7:13-17(NKJV)

Then one of the elders answered, saying to me, “Who are these arrayed in white robes, and where did they come from?”

And I said to him, “Sir, you know.” So he said to me, “These are the ones who come out of the great tribulation, and washed their robes and made them white in the blood of the Lamb. 

Therefore they are before the throne of God, and serve Him day and night in His temple. And He who sits on the throne will dwell among them. 

They shall neither hunger anymore nor thirst anymore; the sun shall not strike them, nor any heat; 

for the Lamb who is in the midst of the throne will shepherd them and lead them to living fountains of waters. And God will wipe away every tear from their eyes.”

The great multitude are those who have accepted Jesus and have come out of the Tribulation.
 

Now as to my original point, this Scripture once again points to a hierarchical setup up in Heaven where not everyone is treated the same.  Why is that important?  In my opinion it is important because it goes to counter those who believe God and Jesus operate under a "socialist" system.  I believe Scripture proves otherwise. 
 

Now should we as Christians use this as an excuse to be mean to people?  Of course not.  But I do think it gives the stamp of morality to a system that mimics God's system by rewarding imitative and punishing laziness and conformity.  "On earth as it is in Heaven" as they say!