In those days, the word "snake" was usually used in a negative context, to describe someone or something evil.

When you look at mythologies of other nations, in the area of the Promised Land, you learn that the snake was a sign of eternity. For example: in the Sumerian story, "The epic of Gilgamesh", the snake stole the flower that gives man eternal life, from Gilgamesh. Another motif of the snake portrays it as one who guards the world, as he helped one of the kings beat an eagle that killed his descendents. In Egyptian mythology the snake named "Nahabu- Kaue" is what the whole world leans on.  

In the Hebrew Bible, we see a very complex figure of the snake, or serpent, as is the case in other nations. Today we are going to ask ourselves what the snake symbolized in the old ages.
 When the people of Israel complained to G-d in the desert, G-d sent those snakes from one hand, but he saved them with snakes from the other hand. For me, this story proves that the snake is not just an evil creature, but also a sign of life and rejuvenation, as we read in Numbers 21:5-9:

 "וַיְדַבֵּר הָעָם, בֵּאלֹהִים וּבְמֹשֶׁה, לָמָה הֶעֱלִיתֻנוּ מִמִּצְרַיִם, לָמוּת בַּמִּדְבָּר

כִּי אֵין לֶחֶם, וְאֵין מַיִם, וְנַפְשֵׁנוּ קָצָה, בַּלֶּחֶם הַקְּלֹקֵל.
 וַיְשַׁלַּח יְהוָה בָּעָם, אֵת הַנְּחָשִׁים הַשְּׂרָפִים,
 וַיְנַשְּׁכוּ, אֶת-הָעָם; וַיָּמָת עַם-רָב, מִיִּשְׂרָאֵל.
 וַיָּבֹא הָעָם אֶל-מֹשֶׁה וַיֹּאמְרוּ חָטָאנוּ,
 כִּי-דִבַּרְנוּ בַיהוָה וָבָךְ--הִתְפַּלֵּל אֶל-יְהוָה,
 וְיָסֵר מֵעָלֵינוּ אֶת-הַנָּחָשׁ; וַיִּתְפַּלֵּל מֹשֶׁה, בְּעַד הָעָם.
 וַיֹּאמֶר יְהוָה אֶל-מֹשֶׁה, עֲשֵׂה לְךָ שָׂרָף, וְשִׂים אֹתוֹ, עַל-נֵס;
 וְהָיָה, כָּל-הַנָּשׁוּךְ, וְרָאָה אֹתוֹ, וָחָי.
 וַיַּעַשׂ מֹשֶׁה נְחַשׁ נְחֹשֶׁת, וַיְשִׂמֵהוּ עַל-הַנֵּס;
  וְהָיָה, אִם-נָשַׁךְ הַנָּחָשׁ אֶת-אִישׁ—
 וְהִבִּיט אֶל-נְחַשׁ הַנְּחֹשֶׁת, וָחָי" 

"And the people spoke against God, and against Moses: 'Wherefore have ye brought us up out of Egypt to die in the wilderness? For there is no bread, and there is no water; and our soul loatheth this light bread. 'And the LORD sent fiery serpents among the people, and they bit the people; and much people of Israel died. And the people came to Moses, and said: 'We have sinned, because we have spoken against the LORD, and against thee; pray unto the LORD, that He take away the serpents from us.' And Moses prayed for the people. And the LORD said unto Moses: 'Make thee a fiery serpent, and set it upon a pole; and it shall come to pass, that every one that is bitten, when he seeth it, shall live. 'And Moses made a serpent of brass, and set it upon the pole; and it came to pass, that if a serpent had bitten any man, when he looked unto the serpent of brass, he lived."

The snake's dualism of good and evil (see , Genesis 49:17, Exodus 4:3, Deuteronomy 8:15  and more) continued until the days of Hezekiah, the king of Judah, who decided to destroy any sign of the serpent from the story above; probably with the intention of removing any potential opponent, as we can see in 2 Kings 18:4- 

"הוּא הֵסִיר אֶת-הַבָּמוֹת, וְשִׁבַּר אֶת-הַמַּצֵּבֹת

וְכָרַת, אֶת-הָאֲשֵׁרָה;

וְכִתַּת נְחַשׁ הַנְּחֹשֶׁת אֲשֶׁר-עָשָׂה מֹשֶׁה,

כִּי עַד-הַיָּמִים הָהֵמָּה הָיוּ בְנֵי-יִשְׂרָאֵל מְקַטְּרִים לוֹ

וַיִּקְרָא-לוֹ, נְחֻשְׁתָּן"

 "He removed the high places, and broke the pillars, and cut down the Asherah; and he broke in pieces the brazen serpent that Moses had made; for unto those days the children of Israel did offer to it; and it was called Nehushtan"

But even in the days of Hezekiah, we can see the snake in a positive aspect; this time his name is "saraph", as written in Isaiah 6:1-3-

"בִּשְׁנַת-מוֹת הַמֶּלֶךְ עֻזִּיָּהוּ

 וָאֶרְאֶה אֶת-אֲדֹנָי יֹשֵׁב עַל-כִּסֵּא רָם וְנִשָּׂא;

 וְשׁוּלָיו, מְלֵאִים אֶת-הַהֵיכָל. 

שְׂרָפִים עֹמְדִים מִמַּעַל לוֹ, שֵׁשׁ כְּנָפַיִם שֵׁשׁ כְּנָפַיִם לְאֶחָד: 

בִּשְׁתַּיִם יְכַסֶּה פָנָיו, וּבִשְׁתַּיִם יְכַסֶּה רַגְלָיו--וּבִשְׁתַּיִם יְעוֹפֵף.

וְקָרָא זֶה אֶל-זֶה וְאָמַר,
 

קָדוֹשׁ קָדוֹשׁ קָדוֹשׁ יְהוָה צְבָאוֹת; מְלֹא כָל-הָאָרֶץ, כְּבוֹדוֹ".

"In the year that king Uzziah died I saw the Lord sitting upon a throne high and lifted up, and His train filled the temple. Above Him stood the seraphim; each one had six wings: with twain he covered his face and with twain he covered his feet, and with twain he did fly. And one called unto another, and said: Holy, holy, holy, is the LORD of hosts; the whole earth is full of His glory."

If you read those verses closely, you can start to understand that in the story of the Garden of Eden, the snake represents not just evil, but maybe also good; for the snake told the woman the truth, and understood that the test wasn't fair!
 If the tree is the tree of knowledge and evil, is it not possible that the character of the snake is also comprised of both seemingly contradicting characteristics? Is the snake, who fought G-d, but who was also smart and crafty, only a negative character, or does the snake also have positive attributes?