Text

When you will build a new house, then you shall make a parapet for your roof, and you shall not place blood in your house, when one will fall from it.

Rashi

When you will build a new house

If you fulfilled the mitzvah of sending of the nest, you will end up building a new house, and you will fulfill the mitzvah of parapet, for a mitzvah draws a mitzvah, and you’ll arrive to a vineyard and a field and to nice garments. Therefore, these parashiot were placed near each other.

A parapet

A wall around the roof. And Onkelos translated a case; as a case that guards that what's in it.

When one will fall

This one is worthy to fall; and nevertheless, his death shall not happen under your hand, for a merit is brought about under the hands of a righteous one, and a...

Ramban

Then you shall make a parapet

The mitzvah of the parapet is new; or it is explained from ...