ברוך שומר הבטחתו לישראל
HaShem pledged to take the Jews out of the Egyptian Exile and He fulfilled his promise. Therefore, we acknowledge this action. Similarly, HaShem promised to Avrohom that He would provide Avrohom with spiritual children. In whom is that promise fulfilled? Obviously, with Yitzchak as it says (Bereshis 21,12) that in Yitzchak he would be called your seed. And we acknowledge the fulfillment of HaShem’s promise.
However, what is so special about HaShem fulfilling his promise? Many people make a promise and fulfill the condition. For example, a King (or a court) has the ability to decree a punishment, let us say for three years in prison. And they would put that person in prison.
But, in reality, humans cannot always fulfill the promise or punishment. For example, if the prisoner dies after one year in prison, the King (or the court) has no ability to complete the three-year sentence.
HaShem always fulfills His promise. Thus, we express our acknowledgment that HaShem fulfills His promises now and in the future. This same concept is expressed in Shmoneh Esreh א -ל מלך רופא נאמן. HaShem is the only doctor capable of faithfully fulfilling His promises about the health and life of the patient.
