Which day is discussed?
Malbim: The day of vengeance.
Why does it say "ha'Kasheh veha'Gedolah veha'Chazakah"?
Radak: The repetition strengthens how the sword will cut off the Goyim in a way that never was. This will be in the war of Gog and Magog.
What is "Livyasan Nachash Bari'ach"?
Rashi citing Targum Yonasan: The king that was aggrandized like Pharaoh, the first king (also refer to 27:1:4:1). Bari'ach is an expression of Pashut (simple) for he was the first.
Rashi: These three nations are esteemed - Egypt, Ashur and Edom, therefore it says about these like it says at the end - "u'Va'u ha'Ovedim b'Eretz Ashur veha'Nidachim b'Eretz Mitzrayim" (13). The nations are compared to snakes that bite. Livyasan Nachash Bari'ach is Egypt, and Livyasan Nachash Akalason is Ashur.
Radak #1: Livyasan is a metaphor for strong Nochri kings. It is the biggest fish in the sea (a whale). It is called also Tanin - "va'Yivra Elokim Es ha'Taninim ha'Gedolim" (Bereishis 1:21). Tanin is Nachash. It says Bari'ach, as if it was Mavri'ach (extends) from one end [of the sea] to the other because it is so big.
Radak #2: Nachash Bari'ach is the Tali (a diameter) that goes from one end [of the Galgal] to the other. Pirkei d'R. Eliezer says that it moves the luminaries.
Malbim: It is the great fish that is like a bolt in the middle of the sea and does not allow anything to pass 1 . The sword will be Kasheh - harder to pass than it.
Perhaps this is like Rashi (Brachos 8a DH k'Piturei) says, that there is places in the Atlantic ocean that do not accept (let pass) anything made of iron. It seems that this is the Bermuda (or devil's) triangle. Planes are careful not to go there, due to all the planes that were lost there mysteriously. (PF)
What is "Livyasan Nachash Akalason"?
Rashi citing Targum Yonasan: The king that was aggrandized like Sancheriv, the second king. Akalason is an expression of doubled, for he was second.
Rashi: Refer to 27:1:3:2.
Radak: Livyasan is a metaphor for strong Nochri kings. It is the biggest fish in the sea (a whale). It is called Akalason, because it is Okem (bends) itself double its great length. It says "Livyasan
What is "ha'Tanin Asher ba'Yam"?
Rashi: It is Tzor, the head of Bnei Esav. It sits in the heart of the sea. Also Kitiyim are called islands. They are Romiyim.
Malbim: This is the sea Tanin (whale). One cannot kill it with a sword. You will defeat it with its weight and its strength. I.e. there is a nation powerful due to the strength of its land - they dwell on tall mountains and fortresses - Nachash Bari'ach. It blocks those who pass. There is a nation powerful due to the length and width of its land, and its many people - Nachash Akalason. And there is a nation powerful due to the strength of its people - Giborim and giants in it - this is the Tanin in the sea.
