Wikipedia describes Kol Nidrei:
Though not a prayer, this dry legal formula and its ceremonial accompaniment have been charged with emotional undertones since the medieval period, creating a dramatic introduction to Yom Kippur on what is often dubbed "Kol Nidrei night".
Why is this so? What meaning behind annuling oaths evokes such emotions? Why is this one of the highlights of the High Holiday prayer; one of the times almost all Jews regardless of background come to Shul?