The purpose of acknowledgement is to ensure the signer of a document is who they claim to be and has voluntarily signed the document.
Jurats/Oaths & Affirmations
The purpose of a jurat/oath and affirmation is for a signer to swear or affirm that the contents of a document are true.
Signature Witnessing
Some states require this to certify that the individual appearing before you is who he or she claims to be and has personally signed the document voluntarily.
