Oneness theologians and teachers often use the fact that there is only one throne, in the heavenly throne room, and that both the Father and the Son are found to be seated upon that one throne. This is a supporting point of Oneness theology since it describes the unified view of the throne occupant.
John Walvoord, former president of Dallas Theological Seminary states: “It is significant that God is not given an anthropomorphic figure in this revelation and does not appear as a man. A part from the fact that He is said to sit on the throne, no description is given except the colors which impressed John.” (The Revelation of Jesus Christ, pg. 105)
Anthropomorphic terms (God's arm, hand, eye, ear, mouth, etc) have symbolic value and are used to ascribe to God some human shape or form. God, who is Spirit (John 4:24), does not have a literal hand or nostril. These are used to help us understand God. As a Trinitarian Walvoord does not need us to imagine Jesus Christ seated upon the throne because that would mean that only one divine person sits upon the Throne. That would go against the idea that there is no "anthropomorphic figure" in this discussion of the One who sits upon the throne.
In Revelation 4:2 the One who sits upon the Throne is Jesus. Here John has reproduced the visions of Isaiah 6 and 1 Kings 22:19. In Isaiah 6 and 1 Kings 22 the Lord is described as "his train filled the temple" and sitting on "his throne" (KJV). The pronoun "his" refers to one person seated upon one throne. From Isaiah to John it is a He who sits upon the throne.
Jesus actually makes it clear in His revelation to John, "The one who conquers, I will grant him to sit with me on my throne, as I also conquered and sat down with my Father on his throne." (Revelation 3:21 ESV) Earlier in the Gospel of John Jesus stated, "He that hath seen me hath seen the Father"; "I and my father are one." (John 14:9; 10:30). Jesus makes it clear that He is the visible expression of the invisible and immaterial Father. This does not mean "Jesus is the Father" since any Biblical discussion retains distinctions without separateness. Consider what the author of Hebrews records:
God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets, 2 Hath in these last days spoken unto us by his Son, whom he hath appointed heir of all things, by whom also he made the worlds; 3 Who being the brightness of his glory, and the express image of his person, and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high; KJV
Log ago God spoke to our ancestors in many and various ways by the prophets, 2 but in these last days he has spoken to us by a Son, whom he appointed heir of all things, through whom he also created the worlds. 3 He is the reflection of God's glory and the exact imprint of God's very being, and he sustains all things by his powerful word. When he had made purification for sins, he sat down at the right hand of the Majesty on high NRSV
1 John 4:9 By this the love of God is revealed in us: that God sent his one and only Son into the world in order that we may live through him. LEB
1 John 4:9 In this the love of God was manifested toward us, that God has sent His only begotten Son into the world, that we might live through Him. NKJV
The two translations above have "one and only" and "only begotten" Son. To say that Jesus was sent should be understood as an expression referring to the mission and authority of the Son. His sending into the world, from the womb of Mary (Galatians 4:4), was no mere "coming into the world". Here John uses Jewish expression to legitimize and authorize to the Son's mission as one sent from God. The Spirit of the Lord was upon the Son who is sent to "proclaim liberty to the captives and recovering of sight to the blind" (Luke 4:18 ESV); is sent to "preach the kingdom of God" (Luke 4:43 ESV) and to be the Savior of the world. (1 John 4:14).
This sending should be understood within the temporal perspective that Jesus Christ experienced. It should at least be the starting point. The “sending” or “coming” is in terms of a commissioning and sending of the only begotten Son of God. A descent from a non-earthly location in the sense of an angel or emanation was probably not on the mind of John here. As the Son of God Jesus was both humanity and deity inseparably and perfectly united. Although God continues to exist beyond the Incarnation God was manifest in the flesh (1 Timothy 3:16). To speak of God in Christ is speak of the person, character and sum total of Deity which was in bodily form (Colossians 2:9).
John recorded that the heavenly throne room had one throne and yet from it come the Father and the Lamb, or Christ. Lighting, thunder, and voices even come from the throne (Revelation 4:5). Yet there is only "one" who sits upon the "one" throne (Revelation 4:2). Only one is described as doing the action of sitting. This is not a logical contradiction but indicates the singular God and His manner of revelation, distinction, and power. Jesus is not a copy but the exact visible representation of the invisible, indescribable God.