en_tn_lite_do_not_use/num/18/15.md

Everything that opens the womb, all the firstborn

These two phrases mean basically the same thing. AT: "Every firstborn male" (See: rc://en/ta/man/translate/figs-parallelism)

Everything that opens the womb

The idiom "opens the womb" means to be the first male that a mother gives birth to. (See: rc://en/ta/man/translate/figs-idiom)

the people must certainly buy back every firstborn son

Instead of sacrificing their firstborn sons, people had to pay the priests for their sons.