“When thou buildest a new house, then thou shalt make a parapet for thy roof, that thou bring not blood [guilt] upon thy house, if any man fall from thence.”
– Deuteronomy 22:8, JPS 1917 Tanach
“Roofs of houses in the ancient Near East were flat and were regularly used for a variety of purposes: drying and storing produce, strolling and socializing, and sleeping in warm weather.” (p.201, The JPS Commentary Deuteronomy). The danger of falling off the roof was a constant risk unless a parapet was put in place around the perimeter of the roof.
The literal translation of the verse is “lest a fallen one should fall.” How can that be? How can one be fallen, even before he falls? The phrasing implies that the one who might potentially fall was already a sinner. Therefore, the fallen one is due punishment from H’Shem, for some sin that had already been committed.
Yet, we are commanded to build a parapet so this “fallen one” does not fall and injure himself on our own roof. Following the commandment, prevents the punishment from being enacted upon a “fallen one,” through neglect, were the homeowner otherwise not as conscientious to put a protective fence in place.
That is to say, that bad things happen through the instrumentation of others who are lacking in character. Yet, G-d’s people are called towards righteousness, in all of our ways. Moreover, we have the responsibility of being considerate, for the sake of others. If something negative occurs, let it not be on our watch.