"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." - Revelation 7:4
Four Angels hold back the four winds - North, South, East and West - at the four corners of the earth. Obviously this is not a vindication of Flat-Earthism - the four corners are obviously referring to the farthest regions attainable by travelling north and south, east and west from a central point - the focus point of all things of course being Jerusalem. So rising from the east with the sun (alluding to the Son and his victory at the cross?) is another angel, who holds back the other angels from hurting the earth, the sea and the trees until he has sealed the servants of God on their foreheads with the seal he carries.
"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. Of the tribe of Juda were sealed twelve thousand. Of the tribe of Reuben were sealed twelve thousand. Of the tribe of Gad were sealed twelve thousand. Of the tribe of Aser were sealed twelve thousand. Of the tribe of Nepthalim were sealed twelve thousand. Of the tribe of Manasses were sealed twelve thousand. Of the tribe of Simeon were sealed twelve thousand. Of the tribe of Levi were sealed twelve thousand. Of the tribe of Issachar were sealed twelve thousand. Of the tribe of Zabulon were sealed twelve thousand. Of the tribe of Joseph were sealed twelve thousand. Of the tribe of Benjamin were sealed twelve thousand." - Revelation 7:4-8
The angel proceeds to seal 144,000 Israelites of all the tribes of Israel - 12,000 of each times 12 tribes is 144,000. These 144,000 Israelites are servants of God - for this reason I believe that these 144,000 represent not a remnant, but the first of many Israelites who will preach the Good News to all. These 144,000 represent God's main front line troops in the battle for Israel's souls, as they finally come to realise their folly in rejecting Christ.
After this John is confronted with a vision of a great multitude of people worshipping God. These are people who have come from great tribulation, and have rinsed their robes to be spotless and holy with the precious blood of Jesus (the Lamb). It would be simple to assume that because the words "great tribulation" are used, this means that this multitude solely represent those described in the Fifth Seal.
However, this fails to bear in mind those Old Testament folk who were brought to heaven by Jesus from Paradise (Abraham's Bosom) at Calvary, nor does it consider those who were raptured (but then again this verse is used as an argument against the rapture despite the first objection). For this reason I believe that this refers to all followers of God - after all, though the persecutions that God's people will undergo throughout the tribulation will be terrible, many have in the past undergone terrible persecution for their beliefs, and it is somewhat belittling to suggest that just because these folk were not under tribulation during this particular period, their tribulations were not "great".