ויגד למלך מצרים AND IT WAS TOLD THE KING OF EGYPT — He sent public officers with them, and as soon as they had reached the three days’ journey which he had fixed for them to go and return, and these perceived that they were not going back to Egypt, they came and told Pharaoh on the fourth day (cf. Mekhilta d'Rabbi Yishmael 14:5:1). On the fifth and sixth they pursued after them: on the night of the seventh day they went down into the sea and on the following morning they (the Israelites) sang the Song of Praise and this was the seventh day of Passover. And that is why we read “The Song” (Exodus 15:1 ff.) as the Scriptural lesson on the seventh day of the Festival (Megillah 31a; Seder Olam 5; cf. Sotah 12b).
ויהפך [AND THE HEART…] WAS TURNED — it was turned (changed) from what it had been, because he had said to them (Exodus 12:31) “Arise, go out from the midst of my people”, and his servants’ hearts were changed because formerly they had said to him, (Exodus 10:7) “How long shall this man be a snare unto us? [let the men go etc.]”. Now, however, they (their hearts) were changed, prompting them to pursue them, because of the property that they had handed over to them (cf. Mekhilta d'Rabbi Yishmael 14:5:3).
מעבדנו means from serving us (i. e. the word is an infinitive with an objective suffix and not a noun signifying “from our service”, which would require מֵעֲבוֹדָתֵנוּ).