Answer and Explanation:
By the above statement, King was metaphorically addressing the noncompliance of the government with the civil rights as stated in the US Constitution for all US citizens as stated in the (14th and 15th) Declaration of Independence and the Reconstruction Amendments which was without race discrimination as at when declared.
King was trying to argue that the US owed its black citizens because it has not kept the promises made to the general American people because it has failed to guarantee the rights of life, right of freedom, and right of the pursuit of happiness.
Instead, the black community had been given a blank check and are left unattended to.