Rev 4:1-5

BEFORE THE THRONE
1 After these things I looked and saw a door opened in heaven, and the first voice that I heard, like a trumpet speaking with me, was one saying, “Come up here, and I will show you the things which must happen after this.” 
Rev 4:1
The first voice which I heard like a trumpet – from Rev 1:10, the voice of the Spirit of Christ, the Angel, Rev 1:1, who is guiding John through this Revelation.

after these things – that is: after the LORD’s Day, this statement signifies that John has been transported to the New Heavens and the New Earth. John’s entire meeting with the Spirit of Christ from Rev 1:7 to Rev 4:1 was in the LORD’s Day. Now the Spirit of Christ calls him up into the New Heavens. This is clear from verse 4, and Rev 5:13.
2 Immediately I was in spirit. Behold, there was a throne set in heaven, and one sitting on the throne 
Rev 4:2
I was in spirit and behold a throne – in Rev 1:10, John was transported by the spirit of God into the LORD’s Day, and now he is about to see heaven thereafter.

One sitting on the throne – we are about to see the same vision of God that Ezekiel saw in Ezekiel Chapter 1.
3 that looked like a jasper stone and a sardius. There was a rainbow around the throne, like an emerald to look at. 
Rev 4:3
Jasper and Sardius stone in appearance – a red colour. In Ezek 1:27, His appearance is described as either “glowing metal” NASB, or “as the colour of Amber” (orange-red) NKJV.  John repeats the word “appearance” as did Ezekiel, emphasizing this as a vision. For as John said, “no one has seen God at any time” (1 John 4:12).

there was a rainbow around the throne – see also Ezek 1:27-28. In Rev 10:1, the Spirit of Christ, as the Angel of God, appears with the rainbow over His head, signifying that He was also “the image of the invisible God,” in this passage.
4 Around the throne were twenty-four thrones. On the thrones were twenty-four elders sitting, dressed in white garments, with crowns of gold on their heads. 
Rev 4:4
24 thrones and 24 elders – we are beyond the LORD’s Day, after the dead in Christ have risen. The number 24 possibly represents 12 elders of the Apostolic church and 12 elders of the Sanctified Church in the end days.
5 Out of the throne proceed lightnings, sounds, and thunders. There were seven lamps of fire burning before the throne, which are the seven Spirits of God. 
Rev 4:5
Seven lamps which are the seven Spirits of God – see Zech 4:2;10.