I.H. Marshall, Jesus the Savior, IVP, 1990, p. 275ff
In modern times we define a host of relations by contracts. These are usually for goods or services and for hard cash. The contract, formal or informal, helps to specify failure in these relationships.
The Lord did not establish a contract with Israel or with the church. He created a covenant. There is a difference. Contacts are broken when one of the parties fails to keep his promise. If, let us say, a patient fails to keep an appointment with a doctor, the doctor is not obligated to call the house and inquire, "Where were you? Why didn't you show up for your appointment?" He simply goes on to his next patient and has his appointment secretary take note of the patient who failed to keep the appointment. The patient may find it harder the next time to see the doctor. He broke an informal contract.
According to the Bible, however, the Lord asks: "Can a mother forget the baby at her breast and have no compassion on the child she has borne? Though she may forget, I will not forget you!"