What are the implications of "Vedarashta Heitev"?
Rashi: Refer to 13:15:1:1***.
What is the meaning of "Nachon ha'Davar"?
Rashi (citing Sanhedrin 29a): It means that the testimonies of the two witnesses match (Mechuvan). 1
Sanhedrin 30b: For cases concerning capital punishment, they must match even for Bedikos (matters not essential to the testimony). For monetary cases, it will suffice if they match for the seven basic Chakiros. A case occurred in which the witnesses said exactly the same, word for word. The Vilna Gaon disqualified them, since 'Mekuvan' means that there are small discrepancies that we can attribute to the fact that witnesses are human and do not perceive everything to the exact millimeter and second. If they say exactly the same, presumably they coordinated to say the same lie! (Cited in Chumash Ateres Rashi.)
Since the Torah writes "be'Yisrael", from where do we know that Geirim and Avadim are also included?
Sifri: We incorporate them from the next Pasuk, which states "Vehotzeisa es ha'Ish ha'Hu" - and not "Vehotzeisa osam" - implying whoever it may be, even Geirim and Avadim. 1
The question arises however, why the Torah then writes "be'Yisrael" in the current Pasuk? See Torah Temimah in Emor Vayikra, 23:43, note 172 DH 'u'Mah she'Darush'.