Yahweh hardened 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 phrase in Exodus 9:12. AT: "caused Pharaoh to became more defiant" (See: rc://en/ta/man/translate/figs-synecdoche and rc://en/ta/man/translate/figs-metaphor)

he would not let them go

"Pharaoh would not let them go"

"Make sure of one thing" or "Be certain of one thing"

Here the word "face" refers to the whole person. AT: "you see me" (See: rc://en/ta/man/translate/figs-synecdoche)

With these words, Moses emphasizes that Pharaoh has spoken the truth. AT: "What you have said is true" (See: rc://en/ta/man/translate/figs-idiom)