Deuteronomy 22:8

When thou buildest a new house, thou shalt make a surrounding fence to thy roof, that it may not be the occasion of blood guilt by the loss of life at thy house, by any one through heedlessness falling therefrom.

The passage of when you buy a new house is juxtaposed to the previous passages, because the commandments concerning residences will apply only after engaging in warfare upon entering the land.

The word railing [Hebrew: maɒ qeh] has no cognates; its meaning is understood from context. One grammarian [it is not certain who is meant, but it could be Yosef Qimḥi — Translator] derived it from “the offenses [Hebrew: aqat] of the wicked” [Psalms 55: 4], and thereby succeeded only in being rather offensive himself.

falling person Scripture employs prolepsis, describing what he becomes. Compare, “the condemned [literally: the dead person] will die” [17: 6], “you strip the naked of their clothing” [Job 22: 6], and also “the sons moved strongly” [Genesis 25: 22]. Countless other words, as well, describe what their referents will become. We do not know whether this is the ordinary Hebrew idiom, or whether they are all prophetic utterances (like “he pursued as far as Dan” [Genesis 14: 14], “to Grapecluster Valley” [Numbers 13: 23], and “therefore a man shall leave his father and his mother, and join with his wife” [Genesis 2: 24]). The commandments of sowing and planting follow the commandments involving a house, because after entering the land, and building a house, one proceeds to sow.

THEN THOU SHALT MAKE A PARAPET FOR THY ROOF. The commandment of the parapet is newly-declared, or it may be explanatory of the prohibition, Neither shalt thou stand idly by the blood of thy neighbor. But the commandment concerning mixed seeds is explanatory, for He has already stated, Thou shalt not sow thy field with two kinds of seed. Now, this [prohibition] implied any place where they are sown; here he added that if a vineyard be sown with mixed seeds that which has been sown ‘tikdash’ (will be forfeited) together with the increase of the vineyard, meaning to say that any benefit is forbidden just like hekdeish [“holy things” belonging to the Sanctuary from which we are prohibited to derive any benefit]. The meaning of ‘pen tikdash’ (‘lest’ thou forfeit) is like ki tikdash (“for” you shall forfeit). So also, And ye shall not go out from the door of the Tent of Meeting ‘pen tamuthu’ (‘lest’ ye die), 10:7. [is like ki tamuthu — “for” you shall die]. Likewise, Neither shall ye touch it ‘pen t’muthun’ (‘lest’ ye die) [is like ki t’muthun — “for” you shall die]. It is possible that the meaning of pen tikdash is similar to ‘pen’ their adversaries should misdeem, ‘pen’ they should say, Our hand is exalted which is like “perhaps.” The verse thus states: Do not sow the vineyard with mixed seeds, for perhaps they will sprout and the whole vineyard will be forbidden to you, for they do not become forfeit [unless they sprout] as we have been taught, “A grain crop [sown near a vine] is rendered forfeit after it has struck root, and grapes, after they have grown to the size of a white bean.”

מעקה, this word is unique in Scripture, constructed from עקה just as מעשה, a deed, action, is constructed from the root עשה, and מראה, from ראה. However, similar sounding words in Psalms 55,4, מפני עקת רשע, “because of the oppression of the wicked; as well as in Amos 2,13 מעיק תחתיכם, “I will slow you down by force,” follow the pattern of such roots as שב and קם.

ולא תשים דמים בביתך כי יפול הנופל, if it were to happen that someone falls off that roof you could not have been the indirect cause, seeing you had put up a protective railing. Had you not done so, your family might bear part of the guilt for such a mishap.