And I saw a great white throne, and him that sat on it, from whose face the earth and the heaven fled away; and there was found no place for them.
Great - in contrast to the "thrones" (Revelation 20:4).
White - emblem of purity and justice.
Him that sat on it - the Son, to whom 'the Father hath committed all judgment.' God in Christ, i:e., the Father represented by the Son, before whose judgment-seat we must all stand. The Son's mediatorial reign is to prepare the kingdom for the Father's acceptance, which having done, He shall give it up to the Father, 'that God real be all in all,' coming into direct communion with His creatures, without a Mediator's intervention, for the first time since the fall. Christ's Prophetical mediation was prominent in His earthly ministry; His Priestly is prominent now in heaven between His first and second advents; His Kingly shall be so during the millennium and at the general judgment.
Earth and ... heaven fled away. The final conflagration precedes the general judgment, followed by the new heaven and earth, (Revelation 21:1-27.)