What is "Mishkani" referring to?
Rashi: It refers to Hashem resting His Shechinah in the Beis-Hamikdash. 1
Seforno and Targum Yonasan: It is referring to the Shechinah, which will rest upon us wherever we will be, as it would have done had Yisrael not worshipped the Golden calf. 2
What does "v'Lo Sig'al Nafshi Eschem" mean?
Seforno: It means that never again, will Hashem reject us, 5 (like He did by the destruction of both the first and the second Beis-Hamikdash).
Rashi: Like "Ki Sham Nig'al Magen Giborim" (in Shmuel 2, 1:21, which means that the shield of the mighty ones ejected the grease (that one smears on shields to prevent arrows and spears from piercing the leather, and to slide off), and as in Iyov, 21:10.
See Ramban, who asks a. what sort of Berachah it is that Hashem will not reject those who perform all the Mitzvos and who do His will, and b. even in the Kelalos (later in Pasuk 42), the Torah writes "Lo Me'astim v'Lo Ge'altim".
Which the Ramban refers to as 'Secrets of the Torah' (See R. Chavel's footnotes).
Because they will be clean of sin (See Ramban, DH 'Aval ha'Inyan Sod'.