What is the meaning of "u'Sh'eriso l'El"?
Radak: [The remainder] will be for his idol.
Malbim: This corresponds to those who think that it is divine. Corresponding to those who think that it merely draws influence, it says 'l'Fislo".
Why does it say "Yisgad Lo va'Yishtachu"?
Radak #1: The matter is repeated in different words.
Radak #2: Yisgad is bending the knees. Yishtachu is [prostrating,] spreading the hands and feet (Brachos 34b).
Radak citing Targum Yonasan: He bows to it and serves it.
Malbim: Yisgad corresponding to those who think that it merely draws influence. Corresponding to those who think that it is divine, "Yishtachu v'Yispalel Elav v'Yomar Hatzileni Ki Eli Atah."