Isaiah uses parallels with the exodus to compare Israel and Egypt. The same words are used to describe the enemy and the call for help that is used when the Israelites were in bondage in Egypt. God would then send someone to save them, just like he sent Moses to deliver the Israelites.
20 It will be a sign and a witness to the LORD of hosts in the land of Egypt. When they cry to the LORD because of oppressors, he will send them a savior and defender, and deliver them.