Of course he is. We know this from all the other clear Scriptures that say just that very thing (1 Kings 22:22, 1 Sam 16:14, Mat 12:24, John 13:27, Acts 5:3, Eph 2:2, etc.).
However, according to John’s vision alone, you wouldn’t really know that the Devil is spirit, would you? In John’s vision of the future the Devil was a dragon and a serpent and yes thrown into a Lake of Fire (with smoke and all).
However, John himself just comes right out and tells us that the dragon/serpent in his vision in reality represented the Devil/Satan. That is exactly what Rev 20:2 means (Rev20:2). Nobody thinks John is saying that Satan will literally become a dragon in the future.
Revelation 20:2 (ESV) 2 And he seized the dragon, that ancient serpent, who is the devil and Satan, and bound him for a thousand years,…
If it weren’t for the fact that John actually parenthetically tells us what these animals represented in his vision (and this had been reliably kept as Scripture for all these years), I’m sure there would be all kinds of wild speculation about which president this “dragon” represented (like helicopters are imagined in Rev). But the point is, nobody with any real aim for the truth thinks the dragon and the serpent John described earlier in his vision is anything other than the Devil himself (Satan of old) as talked about elsewhere in Scripture. So, my point is John clarifies his vision for us. No secret interpretation needed (at least for who the dragon is).
So yes, he’s a spirit in real life. But is the “Lake of Fire” a body of water with flames coming out of it literally? Of course not. Lake of Fire = the second death. Plain and simple. John clarifies this point for us, just like he did with the dragon.
Is it literally a puddle of water somewhere in space filled with flames/fire, or in the inner core of the Earth, or rather is it just like John says it is? He saw it in his vision as some kind of Lake of Fire and even saw the Dragon being thrown into it, sure. Yet, John clarifies for us just exactly what the “Lake of Fire” represented within his vision. Lake of Fire = Second death
Revelation 20:14b (ESV) This is the second death, the lake of fire.
This statement he is making, is not his vision, it’s his interpretation and clarification of the vision. It’s actually very clarifying to this whole book. It clarifies how John’s vision lines up perfectly and harmoniously (just like it had the same Author) with all the other verses like # 53 from Timothy W’s list (that you erroneously accused him of not producing, yet he clearly has listed them in two long posts):
2 Cor 7:10 For the sorrow that is according to the will of God produces a repentance without regret, leading to salvation, but the sorrow of the world produces death.
Since Paul was perfectly familiar with (and knowing full well he was about to experience “physical death”, it’s quite obvious that he means something other than just simply physical death. At least spiritual death or more likely BOTH as second physical death
and a final, eternal, everlasting spiritual death as well. We all experience that 1st physical death, even Jesus, so that cannot be what he meant to contrast here between the lost and the saved final fate.