Rashi: It is an expression of striking.

Rashi: After the Makah He will cure them. Radak - this is so they will recognize that He strikes and heals. When they repent to Hashem and scream to Him, He will accede to them and heal them immediately.

Malbim: Hashem will not conduct with Egypt like with other nations hateful in His eyes - He strikes them in the way of vengeance, to destroy the nation and swallow it. Rather, when He strikes Egypt, it will be in the way of a cure. If they will depart from the straight path, He will strike them to make them put to heart that they sinned. They will repent; Hashem will be appeased, and He will cure them.

Rashi: He will be pleased with them.