There is a Rabbinic tradition that teaches that the three daily prayers, Shaharit, Minhah, and Arvit, originated with the prayer practices of the three avot (patriarchs), Avraham, Yitzhak, and Ya’akov, respectively.  The notion that three different forefathers instituted these prayers, and the fact that three distinct verses are used to ground these practices, also serves to illustrate the different forms that these prayers can take.  Although the eighteen blessings of the Amidah are always the same, we are always changing.  Although we may recite the same prayer formula, the meaning and effect of the prayer experience can and should change as we do.