Bruce Shelley in Christian Theology in Plain Language, writes:
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.
Contracts 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!” (Isa. 49:15).
The Bible indicates the covenant is more like the ties of a parent to her child than it is a doctor’s appointment. If a child fails to show up for dinner, the parent’s obligation, unlike the doctor’s, isn’t canceled. The parent finds out where the child is and makes sure he’s cared for. One member’s failure does not destroy the relationship. A covenant puts no conditions on faithfulness. It is the unconditional commitment to love and serve.
750 Engaging Illustrations.