Menachot 72 - Reaping the Barley On Shabbat

The word "takriv," you will bring, is repeated in the Torah three times. This teaches that although the commandment is to cut barley specifically for that purpose, still, if they found none, but only barley that is already cut, they can use it. Furthermore, even though the commandment is to reap that barley on the night of the first day of Passover, if they forgot or if the barley harvested at night became invalidated, they can still cut it on the following day. Finally, the commandment is to reap and process the barley on that night, even if it happens to be Shabbat and even if they happen to be ritually impure.

However, Rabbi Akiba stated a general rule (talking about circumcision that can also be done on Shabbat) that if some labor can be done before Shabbat, then it should be done before Shabbat. How is that reconciled with above? The above follows Rabbi Shimon's principle that "beloved is the mitzvah done in its proper time." For example, for the daily sacrifice brought on Shabbat they would continue the service and burn its limbs, even though they could have done that later.

Art: Henri-Horace Roland Delaporte - Still-Life with a Carafe of Barley Wine