Akeidat Yitzchak

“Akeidah” – (f., pl. “Akeidot”); The binding; as in “Akeidat Yitzchak,” the “Binding (as a Sacrifice is bound) of Yitzchak, and his offering by Avraham to HaShem, as a sacrifice, according to His Command.” Until, at the last moment, while the sword was already in the air, an Angel of G-d intervened to stop the drama and pointed to a ram, to be substituted for Yitzchak (Bereshit 22:1-19), thus declaring for all time that human sacrifice was in fact abhorred by G-d.

This was the primary expression of faithfulness to HaShem by Avraham and Yitzchak; Avraham, for his willingness to sacrifice his beloved son, although to do that involved terrible contradictions to his previous perception of HaShem and to his teachings concerning the Almighty, and Yitzchak, for his willingness to be sacrificed upon the altar so that his father could fulfill the Command of G-d.

This act of “Mesirat Nefesh,” “Self-Sacrifice,” by Avraham, the father willing to sacrifice his son, even more than Yitzchak’s “Mesirat Nefesh,” who only was willing to give up his life, became the model for Jewish behavior in times of persecution, throughout the ages. And it became also the act that we could point to on “Rosh HaShanah,” the Day of Judgment, as the level of loyalty that our People is capable of.

Taken from: http://www.ou.org/about/judaism/a.htm#akeidah