As we have learned (see daf 27), sacrifices are limited by both time and by place. Thus, someone whose intent was to perform the sacrificial service at the wrong time, will make the korban invalid, and, in fact, the sacrifice becomes piggul – abhorrent (see Vayikra 7:16-18) – and eating of the meat of such a korban will make the person liable to receive karet, a severe punishment at the hands of Heaven. Someone whose intent was to perform the sacrificial service in the wrong place will make the korban invalid, although the person who ate of this meat would not receive karet.
It should be noted that the simple reading of the abovementioned source for this law sounds as if the sacrifice will become invalid if the korban is actually eaten at the wrong time; it is the Sages who determined that this law is dependent on the person’s intent rather than on what was actually done. The Gemara on today’s daf searches for a source for this interpretation.
In the baraita that is quoted by the Gemara, Rabbi Eliezer argues that eating the meat of the sacrifice on the third day, i.e. after the time that it is permitted to be eaten, could not possibly invalidate the korban. Since the korban had already been accepted, how could it become invalid retroactively? The opinion of Aḥerim in the same baraita is that we can understand from the pesukim that it is thought and intent that will invalidate the sacrifice, since the Torah says lo yeḥashev lo – it will not be considered to his credit (see Vayikra 7:18) – which they understand to refer to his own consideration regarding the sacrifice.
The Gemara suggests that Rabbi Eliezer rejects this interpretation of the words lo yeḥashev lo because he uses them as the source for a different halakha, taught by Rabbi Yannai. Rabbi Yannai understood that this passage teaches that if someone had two inappropriate thoughts – e.g. that he planned to eat the sacrifice at the wrong time and the wrong place – that the sacrifice becomes invalid but the person will not be punished with karet, since his intention to perform the sacrificial service in the wrong place already disqualifies the korban without the punishment, making his thought to perform the sacrificial service at the wrong time meaningless.