1 In that
day [yowm] the LORD [Y@hovah] with his
sore [qasheh] and great [gadowl] and strong [chazaq] sword [chereb] shall punish [paqad]
leviathan [livyathan] the piercing [bariyach] serpent [nachash], even
leviathan [livyathan] that crooked [`aqallathown] serpent [nachash]; and he
shall slay [harag] the dragon [tanniyn] that is in the sea [yam].
1 In that day
the LORD with his hard and great and strong sword will punish Leviathan the
fleeing serpent, Leviathan the twisting serpent, and he will slay the dragon
that is in the sea. ESV
Sore means hard or well tempered. Great and strong refers to the absolute power of Gods sword, a sword of war and a sword of justice.
Leviathan, is a reference to the ancient god like dragon. It also means twisted animal. Twisted in mind as well as twisted in body. Its entire existence is twisted and distorted and confused, and of course, evil.
Leviathan is Satan.
The three reference to Leviathan, fleeing serpent, twisted serpent, dragon of the sea, are matched against the three descriptions of Gods sword, namely hard, great and strong.
The sea is generally used to symbolize history. It is in its place where God placed it. Jesus Christ controls history. And even though it storms and screams and seemingly fights to make its own place and redefine history, it is always returned to the boundaries in which God placed it.
Leviathan is spoken of as the enemy who, though is an ongoing adversary, is defeated already. The end game is already determined, it just remains to be played out.
In that day, is of course the final days of history when Satan is defeated, permanently and forever.