The main purpose of the Guarding Readiness Resources Act is to improve the financial management of funds received by the National Guard Bureau when states reimburse it for the use of military property. The act aims to ensure that these funds are properly credited and utilized for specific purposes related to the maintenance and readiness of National Guard units. Key provisions of this act include a requirement that any funds received as reimbursement from states, territories, or the District of Columbia must be credited to the appropriate accounts used for the expenses incurred.