Opening Balance Accounts Receivable and Payable becomes Opening Balance Adjustment... WHY?

Opening Balance Accounts Receivable and Payable becomes Opening Balance Adjustment... WHY?

Whi is it that when you put your Opening Balance Accounts Receivable and Payable they become Opening Balance Adjustment. Why is the reasoning behind this as It is confusing and I am unsure I even understand what this account is? Can someone explain what this account is and why it was done this way. Thanks.