"Thus those who were studying the subject found indisputable proof of the existence of a sanctuary in heaven. Moses made the earthly sanctuary after a pattern which was shown him. Paul teaches that that pattern was the true sanctuary which is in heaven. And John testifies that he saw it in heaven. GC 415.1"
"And the temple of God was opened in heaven, and there was seen in his temple the ark of his testament: and there were lightnings, and voices, and thunderings, and an earthquake, and great hail."
EGW directly references John's vision of the temple in heaven and the ark of the testament, aligning with Revelation 11:19. The passage amplifies the verse by connecting it to the broader concept of the heavenly sanctuary.
In the temple in heaven, the dwelling place of God, His throne is established in righteousness and judgment. In the most holy place is His law, the great rule of right by which all mankind are tested. The ark that enshrines the tables of the law is covered with the mercy seat, before which Christ pleads His blood in the sinner's behalf. Thus is represented the union of justice and mercy in the plan of human redemption. This union infinite wisdom alone could devise and infinite power accomplish; it is a union that fills all heaven with wonder and adoration. The cherubim of the earthly sanctuary, looking reverently down upon the mercy seat, represent the interest with which the heavenly host contemplate the work of redemption. This is the mystery of mercy into which angels desire to look—that God can be just while He justifies the repenting sinner and renews His intercourse with the fallen race; that Christ could stoop to raise unnumbered multitudes from the abyss of ruin and clothe them…
"And immediately I was in the spirit: and, behold, a throne was set in heaven, and one sat on the throne."
Both passages describe a throne in heaven. EGW expands on this by describing the throne's foundation in righteousness and judgment, and its connection to the mercy seat and the plan of redemption. While Revelation 4:2 is a simple statement, EGW builds upon this imagery.