Exodus 15:9

Pharoh the wicked, the hater and adversary, did say, I will follow after the people of the sons of Israel, and will lay waste their camp on the bank of the sea: I will set war in array against them, and kill them, small and great, despoil them of much spoil, bring them back into great captivity, and divide their substance among my people who make war: and when my soul is satisfied with the blood of their slain, I will sheathe my sword, having, destroyed them with my right hand.

THE ENEMY SAID. “I.e., to his people, when he [Pharaoh] was persuading them with words: ‘I will pursue them and I will overtake them, and I will divide the spoil with my captains and my servants.’” Thus the language of Rashi. Now I have seen in the Midrash Chazita:, Note 317), but in Koheleth Rabbah 1:31 and also in the Mechilta of Rabbi Shimon ben Yochai on the verse here. “Thus did Rabbi Yishmael teach: ‘The enemy said: I will pursue, I will overtake. This should fittingly have been at the beginning of the Song, and why was it not written there? It is because there is no strict chronological order in the narrative of the Torah.’” Now Onkelos is of that opinion, for he translated, “the enemy had said,” referring to the beginning of his plan to pursue after them.
In my opinion, by way of the plain meaning of Scripture, this is to be understood in connection with the preceding verses, [all of them together explaining how the destruction of the enemy came about.] First, Scripture said that they sank in the sea and that they went down into the depths. This happened when the waters returned, and covered the chariots, and the horsemen. After that, Scripture reverts to tell how this came about. With the blast of Thy nostrils, which is a reference to the strong east wind,, Verse 21. the waters were piled up, and the deeps were congealed from the beginning. It was because of this that the enemy thought that he would pursue and overtake them in the sea and divide their spoil, and that his lust would be satisfied upon them. But Thou didst blow upon them with Thy wind, and the sea covered them.
Now Moses mentioned this for in this thought of Pharaoh too were discernible the wonderful causation of G-d, Who strengthened the hearts of the Egyptians and turned their counsel into foolishness to come after the Israelites into the sea, as I have explained above. It is for this reason that following that verse, Moses said, Who is like unto Thee, O Eternal, among the mighty, doing great and wondrous things in ways mutually opposed to each other, [such as was done here: with the same hand, He sank the Egyptians and delivered Israel, as mentioned above].

אמר אויב, when they saw the sea turn into dry ground

אריק חרבי, I will empty my sheath by drawing forth my sword. This round about description of someone drawing his sword is not unique. We find something similar in connection with bows and arrows. In Psalms 38,3 כי חציך נחתו בי, literally: “for Your arrows have landed on me,” the meaning is, obviously, “Your arrows have struck me.” David, using poetic language, describes that when the bow has been placed flat on a solid surface in preparation for the arrow to be shot after the bow has been tensed sufficiently, it is aimed and shot so that its arrival at the target represents a “landing.” Psalms 18,35 uses similar language to describe the action of a bow and arrow.