Yom Kippur is wholly a day of purification, in which God removes the burden of our sins accumulated over the past year.
Corresponding to that, we below make a parallel movement of confessing our sins openly and casting them off.
Most of the vows made by a person during the year have little to do with holiness and spiritual elevation; usually they are angry reactions, or attempts to provoke someone.
Life is full of aggravated expressions such as "If you do not do this I shall never speak to you again!" or "I shall never set foot in this house again!"
Often, such statements are halakhically binding vows.
The absolution of vows, and the inner resolution to annul them forever, not only removes obstacles from interpersonal relations but also relieves the spirit of unnecessary burdens, which should be thrown aside, together with all other sins and transgressions.
The phrase "vows and prohibitions" has an even broader meaning.
Our inner freedom is curtailed not only by external factors but even more so by psychological patterns and inner constraints, such as wishes or plans that we build up, and "vows" that we make, so to speak, to ourselves, until we become enslaved by them.
The release from all vows is therefore a ceremonial act of freeing oneself from these chains and granting one's soul the liberty to stand before God without this cumbersome burden.
The Kol Nidrei ceremony, then, has a deep and spiritual meaning that gives the worshipper a feeling of elevation of soul and freedom of spirit in preparation for the day of pardon and forgiveness.
–Rabbi Adin Steinsaltz
From A Guide to Jewish Prayer, p. 200, by Rabbi Adin Steinsaltz