"one who passes his son or daughter through fire": This tells me only of his son or his daughter. Whence do I derive (the same for) the son of his son or the son of his daughter? From (Vayikra 20:3) "for of his seed he has given to the Molech."
— But still, here it is written "through fire," and there, "the Molech." Whence do I derive what is written here as applying there, and what is written there as applying here? — It is written "passing" (here), "passing" (there, Vayikra 18:21) for an identity (gezeirah shavah), viz.: Just as "passing" here is through fire, so, "passing" there is through fire. And just as "passing" there is to the Molech, so, "passing" here is to the Molech. In sum, (to be liable), he must hand over (his child) and pass him through fire to the Molech. Both verses are necessary (to tell us this); if not, we do not know it.