Having taught the Mitzvah of "Lo Sateh" in Parshas Shoftim, 16:19, why does the Torah repeat it here?
Rashi: The Torah in Shoftim referred [even] to tilting the Din of the wealthy, and it repeats it here to add an additional La'av 1 for [tilting the judgment of the poor. 2
Seforno: It is a specific warning to take care that convert and orphan litigants are not struck dumb (and unable to present their case) due to their lowly status.
Rashi: Since it is relatively easy to pervert their judgment. Refer to 24:14:4:2**. See also Torah Temimah, note 150.
As most converts and orphans are. Targum Yonasan inserts 'Almanah' here, even though the Torah does not - See Na'ar Yonasan.
What sort of security is the Torah discussing?
Why does the Torah forbid taking specifically the garment of an Almanah as a security?
Targum Yonasan: So that people should not slander the creditor when he goes to her house each night or each morning to return it to her. 1
Bava Metzi'a. 155a: To add a second La'av on someone who takes the garments of an Almanah, irrespectiv of whether she is rich or poor. 2
Why does the Torah warn three times against afflicting [or tilting judgment against] Geirim (here, in Shemos 22:2, and in Vayikra 19:36)?
Rosh (citing Bava Metzi'a 59b): Because Geirim are prone to return to their evil ways (whcih they will be encouraged to do if they are wronged). 1
Rosh (Ibid.): Some say that the Torah warns about this forty-eight times.Yalkut Shimoni (Rus 601). Bava Metzi'a 59b says thirty-six or forty-six times. Ra'avad, in Shitah Mekubetzes (59b)