Here "heart" refers to Pharaoh. His stubborn attitude is spoken of as if his heart was hard. AT: "will cause Pharaoh to be stubborn" (See: [[rc://en/ta/man/translate/figs-synecdoche]] and [[rc://en/ta/man/translate/figs-metaphor]])
The word "Israel" here represents all the people of Israel. AT: "The people of Israel are my own children" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Here the people of Israel are spoken of as if they were a firstborn son who causes joy and pride. AT: "is like my own firstborn son" (See: [[rc://en/ta/man/translate/figs-metaphor]])