When the Torah teaches that it is forbidden to eat grain from the new harvest (see Vayikra 23:14), it appears to offer two separate mechanisms for permitting the new crop. According to the Torah “…neither bread, nor parched corn, nor fresh ears” can be eaten –
– until this selfsame day,
– until you have brought the offering of your God.
Thus it appears that the arrival of the day itself permits the new harvest, yet there is also the element of waiting until after the korban ha-omer is brought.
Rav and Shmuel both explain the passage as follows. When the Temple stood and the omer offering was brought on the second day of Pesaḥ (the 16th day of Nisan), the new crop became permitted only after the korban ha-omer. Following the destruction of the Temple, the dawn of the 16th day of Nisan permitted the new crop to be eaten.
According to the Mishna, during the time of the Temple, Jews who were far from the Temple could assume that by mid-day the korban ha-omer would have been brought, and they were permitted to begin eating from the new crop. Following the destruction of the Temple, Rabban Yoḥanan ben Zakkai established a rule that forbade eating from the new crop until the morning of the 17th day of Nisan. His reasoning was that when the Temple is rebuilt – speedily in our days! – people would mistakenly think that they can begin eating from the new grain on the morning of the 16th, not realizing that they were only permitted to do so in the past because no korban ha-omer could be brought. In order to keep them from that mistake, he did not permit the new harvest until the following day.
Rabbi Yoḥanan and Reish Lakish disagree with Rav and Shmuel, arguing that even when the Temple stood the new crop became permitted with sunrise on the 16th of Nisan. Nevertheless there was a special mitzva to wait until after the korban ha-omer was brought before beginning to eat.