וַיְחַזֵּ֣ק יְהֹוָ֗ה אֶת־לֵ֤ב פַּרְעֹה֙ מֶ֣לֶךְ מִצְרַ֔יִם וַיִּרְדֹּ֕ף אַחֲרֵ֖י בְּנֵ֣י יִשְׂרָאֵ֑ל וּבְנֵ֣י יִשְׂרָאֵ֔ל יֹצְאִ֖ים בְּיָ֥ד רָמָֽה׃
永恆者使埃及王法老的心剛硬，他就追趕以色列人；那時以色列人正高舉著手，昂然出去。
Rashi
ויחזק ה׳ את לב פרעה AND THE LORD ALLOWED THE HEART OF PHARAOH TO BE HARDENED — the meaning is, that he was in doubt whether to pursue or not, and He hardened his heart to pursue (Mekhilta).
Rashbam
יצאים ביד רמה, they had not started to worry at all until they saw Pharaoh and his army pursuing them. At that point, וייראו מאד, they became very much afraid.
Sforno
ובני ישראל יוצאים ביד רמה, the meaning of the word רמה here is similar to the meaning of the same word in Deuteronomy 32,27 ידינו רמה, where it means: “our own hand has prevailed.” At the time of their departure they had been confident of their ability to defeat Pharaoh and his military machine as they were much stronger in numbers. The verse teaches that they were relying on their numbers instead of considering their total lack of experience in the art of war. They would have had every reason to fear the numerically inferior Egyptians who had all this experience going for them.