There are several things that are happening here and creating the context might shed some light. However for time sake I will have to plug in verses at a later date
The serpent of old (satan) was a cherub/seraph or a serpentine creature.
He was also a son of God or an elohim.
Jesus says in John 17 that prior to Creation He had a glory. Jesus was also the angel of the Lord or if you like a cherub/seraph as far as all the other “angels” heavenly hosts were concerned.
Jesus was a member of the Godhead that represented the invisible God or we know Him as the Father.
From satan’s vantage point Jesus was the same as himself. Mostly because Jesus had taken off His divine glory prior to Creation. Jesus has at least four different states of being.
- Prior to Creation, glorified God
- After Creation, God but without His glory in appearance a cherub
- Incarnation, God in a non glorified humanlike body
- After resurrection, God in a glorified body.
In satan’s eyes satan wanted to be like the most high and says as much in Isaiah. If the ‘angel of the Lord’ (Jesus), whom the demons knew to be the son of God, if He could be God, why couldn’t satan himself also be God? Consider the train of thought satan might have had.
This was bugging him, that the invisible God was withholding from him the ability to be God too just like this other cherub (Jesus) was God. Lucifer might have even had a higher standing than the angel of the Lord or equal standing other than that title of God.
Further Adam was given dominion over the whole of God’s creation, but Adam was inferior according to Psalm 8 to the heavenly hosts because human beings were not created immortal as Psalm 82 points out the sons of God were. Also the tree of life being in the garden would serve no purpose if Adam was immortal.
So to answer your question
In view of the fact that satan was envious of this one cherub who was God and was called the son of God, satan was convinced that God was hiding something from him that prevented him from also being God like this cherub (Jesus).
When he confronted Eve, satan was merely projecting his frustration onto Eve. He was convinced that God was hiding something from him and if Eve would eat of the forbidden fruit then she too would at least know as much as he knew. Certainly satan had skills and knowledge intuitively that Adam and Eve had no idea about.
It’s possible that satan was banking on eating the fruit himself to gain this knowledge but couldn’t risk ruining his chances. He is extremely shrewd.
Everything he achieves is through legal technicalities and he perpetuates most of his success by keeping people in the dark. If people could know how weak his position actually is, his bluff would be called and he’d lose a lot of ground.
The idea that satan might have wanted to eat of this forbidden fruit isn’t far fetched considering manna was called the food of angels and satan is an angel. Therefore the implication is that angels eat (at least something).
By deceiving Eve to eat, and bringing sin into the world satan stole the dominion from man and supplanted God by establishing himself as god over God’s creation. On technicality if God were to justly apply justice to satan then God would be forced to also judge mankind. So instead of immediately effectuating justice and destroying all of humanity through Adam, God allowed humanity to perpetuate in a fallen state with the intention that every individual could chose God on an individual basis, where Adam has failed. He even provided the ultimate sacrifice freely, which essentially gave God the legal right to take full rights and dominion back.
And the most remarkable of all is that God intends to give dominion right back to man who lost it in Eden, God is giving mankind dominion in the new era to come when there will be a new heaven and a new earth.
Just to summarize, satan was bluffing, satan had no idea if Eve would be like God or not, but he was willing to deceive Eve into eating the fruit to see what would happen.
Adam and Eve were already like God because they were made in His image. God does not ‘know’ (experiential) evil because He has never committed it.
Also it’s curious that satan is said to use elohim you will be like elohim. It’s as if he is enticing Eve to achieve something he has, which is the status of an elohim, something she doesn’t as a human. He was offering her something he couldn’t offer her but was profiting from the fact that he was an elohim even if he was The Elohim. It’s almost reads like he was pretending to be god himself in those moments. You won’t die, look I’m an elohim I if you want to be like me (just like I am like that cherub who visits you every day walking in the garden, that cherub who is called God) then all you need to do is eat the fruit. And Eve was deceived.