What essential document must the bank have on file for many reasons beyond just writing checks?

The essential document that the bank must have on file, particularly related to a checking account, is your signature. This is crucial for several reasons. Primarily, your signature serves as a means of authentication, allowing the bank to confirm that transactions are being authorized by the account holder. When you write a check, the bank compares the signature on the check with the one they have on file to ensure that it matches. This helps prevent fraud and unauthorized withdrawals.

Additionally, signatures are also important for various account-related activities, such as opening new accounts, applying for loans, or making changes to your account. Ensuring the bank has your signature on record allows them to maintain security and accountability in all transactions associated with your account. In comparison, while social security numbers, legal documents, and employment history may be relevant to a bank's overall assessment of an individual, they are not as directly tied to the fundamental operations of a checking account and the authorization of checks and transactions.