Re: Okay, here's the thing (Belgariad related with some spoilers)
Have you considered the effect Polgara succumbing to Torak would have had on Garion (and the others)? If this woman, who epitomised everything about resistance, power and overcoming to Garion was made vulnerable and pliable by Torak then how do you feel Garion would have reacted? Would he have been able to summon any will at all?
I envisioned it as being the event which added that little bit of extra steel into Garion's back.
The 2 prophesies had to have willing vessels otherwise it would have been cheating... I don't think Garion would have really been able to answer the "are you ready?" question with a yes if he saw his Aunt Pol standing there cheering on Torak!