There are some basics which you need to consider here; that change the whole precept of the question.
All Scripture is quoted from the King James translation.
- God is omniscient!
God knew from before he created the Angels; exactly how all things would unfold for Eternity.
- God is Omnipotent!
God is all powerful, he has the power to alter any particular action at any particular time.
- God is omnipresent!
God is not subject to time and space, God is of the Spiritual realm and as such is everywhere at once.
So if we consider the three things above, our questions should be changed from "why does God allow " to "how does this particular incident fit into God's overall plan". The truth is we mere mortals will never be able to understand God or his ways or his thoughts.
Isaiah 55:8 and 9 For my thoughts are not your thoughts, neither are your ways my ways, saith the LORD. For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts.
We then, as mere mortals, must accept the fact that God is so far above us that whatever his plan to is to achieve when it reaches its final conclusion we will never know this side of heaven and possibly not even then. We can however find some clues in what has transpired since God initiated his plan. We can also possibly obtain a few clues from God's word concerning the future.
So let's go back to your original question concerning the serpent in the garden; of the fall and Eve; and all of that. In as much as I can understand: the creation came on the heels of the war in heaven.
Revelation 12:7 through 9 And there was war in heaven: Michael and his angels fought the dragon; and the dragon fought and his angels, And prevailed not; neither was their place found any more in heaven. And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.
And in order for Satan and the rebellious angels to be exiled to earth it would have to have come after Genesis chapter 1 verse 1.
Genesis 1:1 In the beginning God created the heaven and the earth.
As to whether the serpent who deceived Eve was only a serpent, or Satan masquerading as a serpent. We are not told, however. According to the apostle Paul in his second letter to the Corinthians, it could have been either.
2nd Corinthians 11:13 and 14 For such are false apostles, deceitful workers, transforming themselves into the apostles of Christ. And no marvel; for Satan himself is transformed into an angel of light.
It appears to me, that the real lesson we should learn from this is; that in the beginning God created both the Angels and a man with free will. And that when given the opportunity they both rebelled against God's authority. When Adam and Eve disobeyed God in the Garden they introduced into mankind what I consider to the "me" concept. What I mean by that is that up until that time. Man was sublimely happy, secure, and at ease in the presence of God. Following man's initial disobedience, we find that man is no longer comfortable in the presence of God as God created him.
Genesis 3:7 and 8 And the eyes of them both were opened, and they knew that they were naked; and they sewed fig leaves together, and made themselves aprons. And they heard the voice of the LORD God walking in the garden in the cool of the day: and Adam and his wife hid themselves from the presence of the LORD God amongst the trees of the garden.
Some of my fondest memories, are from when my children and grandchildren crawled up into my lap and felt so secure and well cared for that they just went to sleep. while at the same time some of my most hurtful memories are when those same children and grandchildren rebelled. The reasons for these reactions is because of my love for them. I cannot believe that it would be any different with God. I am sure of this; that when both the Angels and man rebelled against God it hurt him deeply because God is love. I am likewise of the opinion that God had the same feelings that I felt; before that rebellion by either the Angels or man.
However be that as it may, those are my thoughts, and you must come to your own conclusions.
We can use the same analytical logic on any passage in the Old Testament's and try and find out, the role these incidents play in the overall plan of God. For instance we can analyze the story of David and Goliath as depicted in 1st Samuel chapter 17. I will not quote it here for the sake of brevity.
Two questions arise using this type of analytical logic.
Did God said through his omnipotence direct the stone and from David's slingshot to its final destination in Goliath's forehead?
Or did God through his omniscience align circumstances so that David could through his own learning be able to so accurately throw the stone that it would hit the exact Mark aimed at.
Whichever of these two God chose, makes very little difference, the point here being that God fore ordained how this particular situation would play out. And the lesson for us would seem to be that man can overcome evil but not without the help of God.
Another example of using this logic in analyzing a passage is in the Story of Abraham and the sacrifice of Isaac.
Genesis 22:1 through 22:13. Again I will not quote them for the sake of brevity, but if you are unfamiliar with it I heartily suggest you read it.
Genesis 22:1 And it came to pass after these things, that God did tempt Abraham, and said unto him, Abraham:
Right off the bat and our first question comes up Why does God who is omniscience decide to tempt Abraham, knowing already what Abraham's reaction would be?
There are some questions to which we simply have to answer: because God is sovereign, and this may be one of them. We could on the other hand wonder if God in his great love is verifying Abraham's faith or not. In view of the following two Scriptures this may seem more feasible.
Genesis 22:7 and 22:8 And Isaac spake unto Abraham his father, and said, My father: and he said, Here am I, my son. And he said, Behold the fire and the wood: but where is the lamb for a burnt offering? And Abraham said, My son, God will provide himself a lamb for a burnt offering: so they went both of them together.
The significance of this passage lies in that Abraham so depended upon God that he believed that even if he were to take the life of Isaac God would replace that life somehow and Isaac would not be lost to him. This compares to the basic hope of Christianity, that being that that even though we have all sinned and come short of the Glory of God, Jesus death on the Cross will bring our Souls back into Eternal life.
So to answer your question:
Was the serpent's temptation necessary for Eve to sin?
The answer to that, in my humble opinion, whether or not the It was necessary for Eve to sin, it was necessary in order for God's plan to unfold as he intended it to.
Although this has nothing to do with the answer to your question I am adding a to help you understand my answer.
Having used this particular analogy trying to understand how God wanted his Scriptures to be understood; for nearly a decade, I have come to my own conclusion that God's overall plan is to restore heaven to it pre-rebellion state. And that Heaven which I feel is described in Revelation chapters 21 and 22 is so desirable to me that it is worth throwing away all other things, all other glories, all of the riches, and any other thing; which would prevent me from being there.
I am so enthralled with this that I'm trying with all my might, to be that little child who crawls up in God's lap and forgets about all other things;
Again those are my conclusions and you must come to your own.