Because they are so washed white; for without it they could never have entered Gods holy heaven.1
before the throne of God
The entire thrust of Scripture, from Genesis to Revelation is the restoration of man to full intimacy with God. These occupy a position of great blessing in their proximity to the throne. By the sovereignty of God, these elect did not come to faith prior to the rapture , but endured the most difficult time for people of faith of all history. Even so, they remained steadfast in their testimony and overcome the adversary (Rev. Rev. 12:11+).
serve Him day and night in His temple
Their ministry is reminiscent of the four living creatures: they do not rest day or night, saying: Holy, holy, holy, Lord God Almighty, Who was and is and is to come! [emphasis added] (Rev. Rev. 4:8+). These who come out of the Great Tribulation may have a different ministry than that of the Church which is caught away prior to this time.
As their calling and service differ from ours, so does their destiny. We, as the bride with the Bridegroom, sit upon the throne to rule and reign with the Lord of Glory. Our destiny is said to be that of rulers and judges. We are to be kings and priests (1Cor. 1Cor. 6:2-3; 1Pe. 1Pe. 2:9; Rev. Rev. 1:6+). The 144,000 are to be the glorious bodyguard, the retinue of the Lamb, following Him whithersoever He goeth (Rev. Rev. 14:4+). The destiny of the Gentile multitude, however, is that of temple servants.2dwell among them
Dwell is σκηνώσει [skēnōsei] : Literally live or camp in a tent.3 Used by John of Jesus incarnation when the Word became flesh and dwelt among us (John John 1:14). This word only appears in the NT in Johns gospel and this book (John John 1:14; Rev. Rev. 7:15+; Rev. 12:12+; Rev. 13:6+; Rev. 21:3+), providing evidence that the books share the same authorship. Their enduring faith in the midst of the Great Tribulation provides a great testimony to the power of God and results in His dwelling among them. They realize the ultimate goal of the eternal state: And I heard a loud voice from heaven saying, Behold, the tabernacle of God is with men, and He will dwell with them, and they shall be His people. God Himself will be with them and be their God (Rev. Rev. 21:3+). As the psalmist said, In Your presence is fullness of joy; at Your right hand are pleasures forevermore (Ps. Ps. 16:11).
He that sits upon the throne shall spread his tabernacle over them. The A.V. reads, shall dwell among them; a poor and utterly inadequate rendering of the divine thought herein expressed. God spread His tabernacle over the tent of meeting of old, which thus became the centre and rest of the thousands of Israel. It covered them in the desert. Two millions and a half peoplethe typically redeemed host of Jehovahwere sheltered from scorching suns and winters blasts, by the huge canopy which God spread over them; it was the nations glory and defense.4His dwelling presence is directly tied to the promises which follow that the sun shall not strike them, nor any heat. His dwelling among them is to be understood as a secondary truth, besides what is expressed, namely, His being their covert.5
When the Lord has washed away the filth of the daughters of Zion, and purged the blood of Jerusalem from her midst, by the spirit of judgment and by the spirit of burning, then the LORD will create above every dwelling place of Mount Zion, and above her assemblies, a cloud and smoke by day and the shining of a flaming fire by night. For over all the glory there will be a covering. And there will be a tabernacle for shade in the daytime from the heat, for a place of refuge, and for a shelter from storm and rain. (Isa. Isa. 4:4-6) [emphasis added]
1 A. R. Fausset, The Revelation of St. John the Divine, in Robert Jamieson, A. R. Fausset, and David Brown, A Commentary, Critical and Explanatory, on the Old and New Testaments (Oak Harbor, WA: Logos Research Systems, Inc., 1997, 1877), Rev. 7:15.