Just because he was called Serpent of old does not mean he was the serpent before the garden..that could be a reference to being the serpent of the old stories of the creation.
The oldest serpent in the Bible - is the one in the tree.
Rev 12
9 So the
great dragon was cast out,
that serpent of old, called the
Devil and Satan, who deceives the whole world; he was cast to the earth, and his angels were cast out with him.
Does not leave us any room for "was a good serpent in Eden but then later turned bad" --
We get no indication of when he actually fell in the Bible.
We know that at the time that he appears in the Bible - tempting Eve - he is the dragon, Devil, Satan, Serpent of old.
We know from Rev 12 that his real war is with Michael - and that in reality it is a war between Satan and Michael that also expands out to war that includes humans.
In Job 1 and 2 - the humans are being protected by God - and attacked by Satan who tries to work the system against them.
In Gen 2 - the humans are told that they can pretty much go anywhere - except the tree of knowledge -- they may not eat of it.
Problem you have is that if you take the punishment of the serpent in Gen 3 as to punish a creature and turn it into a snake to slither on the ground, then Rev 12 has issues in taking the reference of Satan and the serpent of old being the serpent in Gen 3. Because if all God did in Gen 3 was punish a creature, then it was not Satan who tempted Eve, but just some creature.
In Genesis 3 there are several things stated about the serpent as the Devil - and the serpent as a creature.
Gen 3
Now the serpent was more cunning than any beast of the field which the Lord God had made.
And he said to the woman, “Has God indeed said, ‘You shall not eat of every tree of the garden’?”
2 And
the woman said to the serpent, “We may eat the fruit of the trees of the garden; 3 but of the fruit of the tree which
is in the midst of the garden, God has said, ‘You shall not eat it, nor shall you touch it, lest you die.’”
13 And the Lord God said to the woman, “What
is this you have done?”
The woman said, “
The serpent deceived me, and I ate.”
14 So the
Lord God said to the serpent:
“Because
you have done this,
You
are cursed more than all cattle,
And more than every beast of the field;
On your belly you shall go,
And you shall
eat dust
All the days of your life.
15 And I will put
enmity
Between you and the woman,
And
between your seed and her Seed;
He shall bruise your head,
And
you shall bruise His heel.”
=========================
That is the proto evangel
http://www.equip.org/bible_answers/significance-proto-evangel-genesis-315/
The devil is at war with the woman and her seed - the church and church members -
And in the highest sense - the seed of the woman is Christ.
The devil is also at war with Christ.
Christ bruises the head of the serpent on the cross - overcoming Satan - providing salvation for mankind. And then at the 2nd coming again he bruises Satan - and again in rev 20 the lake of fire - Satan's deadly wound - final.
But the serpent bruises his heel - tormenting Christ at the cross.
As for the literal serpent. - the animal, the species is doomed to slither along the ground from that point on. As a testimony to mankind about the fall of man.
What is more - the serpent is talking - this is purely a feature of Satan's use of that animal at the time.
Just as the case with Baalam's donkey - that speaks to Baalam not because donkeys have that ability - but because of some supernatural use of the donkey by God or an angel.
You could say that Satan possessed the serpent and was speaking for it. But then why would God punish something that did not have any control over it and not punish Satan for causing doing the tempting?
The proto-evangel tells satan he will lose - that Christ the seed of the woman - will defeat him.
15 And I will put
enmity
Between you and the woman,
And
between your seed and her Seed;
He shall bruise your head,
And
you shall bruise His heel.”
Satan is also told that "God puts enmity" war - "between the seed of the woman and the seed of the serpent" - Instead of Satan "winning" mankind as he won over 1/3 of the angels that were totally enslaved to his evil dictates - as brothers in rebellion - mankind would not be wholesale sold out to Satan. There would be a supernaturally inserted "emnity" - discord between the kingdom of Satan and the world of mankind.
in Christ,
Bob