en_tn/exo/07/03.md

harden Pharaoh's heart

Here "heart" refers to Pharaoh. His stubborn attitude is spoken of as if his heart was hard. See how you translated this in Exodus 4:21. Alternate translation: "will cause Pharaoh to be stubborn" (See: rc://en/ta/man/jit/figs-synecdoche and rc://en/ta/man/jit/figs-metaphor)

many signs ... many wonders

The words "signs" and "wonders" mean basically the same thing. God uses them to emphasize the greatness of what he will do in Egypt. (See: rc://en/ta/man/jit/figs-doublet)