What is Rechilus? Why does the Torah always present it together with a Lashon of "Halichah" (See for example, Yirmiyah, 6:28)?
Rashi, Ramban 1 and Rashbam: 'Rechilus' is the spreading of negative gossip that Reuven learns about Levi in Shimon's house. What generally happens is that Reuven goes from house to house, digging out scraps of derogatory information about others, which he subsequently passes on as he makes his rounds. 2
Ramban: "Rechilus" is from the same root as "Holchei Rachil 3 (with reference to peddlers, who travel from place to place to sell their wares). 4 By the same token, Holchei Rachil tend to go from place to place peddling their gossip 5
Targum Yonasan: Rechilus is synonymous with Lashon ha'Ra. 6
The word 'Rachil' is equivalent to 'Ragil' - since it entails going on foot from one house to another - and a 'Chaf' and a 'Gimel' (which both sound from the same part of the mouth) are interchangeable. It seems that it was also customary for the recipient of the news to provide a snack (a sort of 'le'Chayim') to establish his guests integrity, which explains why Targum Onkelos (and Targum Yonasan) translates "Lo Seilech Rachil" as 'Lo Seichul <i>Kurtzin' (See also Dani'el 3:8 and Berachos, 58a). Rashi adds that the reason that Onkelos calls it 'Kurtzin' (a wink - See Mishlei, 6:13) is because they would wink and make signs to one another, so that others would not understan. See Ramban, who rejects Rashi's interpretation of Targum Onkelos outright. In fact he (and the Rashbam) interprets 'Lo Seichul <i>Kurtzin' as 'Do not announce Rechilus' (See Targum Yonasan, Shmuel 2. 22:14). See Ramban (DH 'Aval Ikar').
Rashi too, adds this point to his explanation of 'Rechilus'.
And what is the definition of "Lo Sa'amod al Dam Re'eicha"?
Rashi: It is a prohibition against seeing a fellow-Jew dying and doing nothing about it - there where he is able to save him.
Rashbam: It means that one is obligated to save a fellow-Jew from his attacker, even if it means killing the attacker in the process.
Targum Yonasan: It means that a witness should not refrain from testifying in Beis-Din on behalf of one's fellow-Jew.