en_tn_lite_do_not_use/exo/04/23.md

you have refused to let him go

The word "him" refers to the people of Israel as God's son. Alternate translation: "you have refused to let my son go" (See: rc://en/ta/man/jit/figs-metonymy)

I will certainly kill your son, your firstborn

The word "son" here refers to the actual son of Pharaoh.