The Mishnah (43a) brings a disagreement between the Tanna Kamma (=first) and Rabbi Shimon with regard to a question about the application of pigul – inappropriate thoughts relating to time regarding a given sacrifice – to an animal that was to be brought on the inner altar but was being prepared in the outer courtyard. The Gemara on yesterday’s daf (=page)brings another opinion, that of Rabbi Elazar in the name of Rabbi Yossi ha-Galili. The concluding sentence on yesterday’s daf was Rav Nahman quoting Rabbah bar Avuha in the name of Rav who said that the halakhah follows this last opinion.
Reacting to this ruling, Rava asks hilkheta le-meshiha?! – are we establishing halakhic rulings for Messianic times, i.e. when the Temple will be rebuilt? Abayye responds to him by asking whether it would be appropriate to avoid learning any topics about the Temple service, since all of it should be considered hilkheta le-meshiha. Rather, Abayye argues, we study all aspects of Torah, even those that are not applicable since we are commanded – and rewarded – for Torah study. Therefore it is appropriate to learn the laws of the Temple service for that same reason. Rava replies that his question was why there is a need for a final ruling on these matters, since they are not practical at this time.
Tosafot point out that there are many places in the Gemara where a particular halakhic conclusion is reached regarding a question about the Temple service, but they argue that it is only in cases where the ruling will have practical ramifications as well. They also bring the opinion of Rabbenu Hayyim ha-Kohen who suggests that there is a particular problem with rulings regarding forbidden acts in the Temple, since there is no reason to rule about a forbidden act in Messianic times.
As a general principle, the study of any area of Torah in an attempt to understand the Torah’s true intent is a valuable exercise, whether the topic is practical or esoteric. Nevertheless, reaching a halakhic conclusion can be viewed as bowing to necessity, inasmuch as we need to decide how to act in a given case. Therefore there is no problem with studying the laws of pigul, the only surprise is to find that there are final rulings about those laws, since they are not applicable today.