John Calvin Commentary Deuteronomy 22:8

"When thou buildest a new house, then thou shalt make a battlement for thy roof, that thou bring not blood upon thy house, if any man fall from thence." — Deuteronomy 22:8 (ASV)

This precept also relates to the preservation of human life. We know that the roofs of Jewish houses were flat, so that people could freely walk on them. If there were no railings around them, a fall would have been fatal, and every house would often have become a house of mourning.

God, therefore, commands that the edge be fortified with battlements, railings, or other enclosure, and accompanies this injunction with a severe denunciation. For He declares that the houses would be defiled with blood if anyone should fall from an unenclosed roof.

Now, if guilt were thus contracted by mere incautiousness, it therefore shows how greatly He abominates deliberate cruelty. And, if it was necessary for everyone to be so concerned for the lives of their neighbors, it reveals how criminal it is to injure them intentionally and with hostility.