Our Gemara on Amud Aleph, based on a scriptural proof, discusses the principle that for an oath to be valid, it must concern something where there are no pre-existing Torah obligations. Thus, if one made an oath to perform a mitzvah, it would not be binding since he was already obligated in the mitzvah. Similarly, an oath to refrain from performing a mitzvah would not be binding. (See Shulchan Aruch YD 232:6.)

There is a well-known Mishna at the beginning of Yoma that describes an uncomfortable ordeal that the Cohen Gadol had to perform along with the sages. Since there was a strong sub-sect of Cohanim who were Sadducees, the sages feared that the Cohen Gadol might be a crypto-Sadducee and seek to perform the ritual in the Holy of Holies according to their doctrine rather than the correct tradition. The verse states (Vayikra 16:2): “For I appear in a cloud over the cover (of the Ark).” Our sages interpreted this cloud to be the divine presence. However, the Sadducees took a more literal interpretation and believed that the Cohen Gadol should light the incense prior to entering the Holy of Holies. The Sadducees did not give credence to the Oral Tradition of the sages, but they were proud Jews and observed their religion according to the dictates of their conscience. Since both groups shared the same holy Temple, there could be only one correct way to perform the service. The rabbis feared the Cohen Gadol might be a crypto-Sadducee and, in his misplaced religious zeal, perform the service according to his tradition. (By the way, a similar event actually occurred where a Sadducee cohen performed the Temple service according to his dictates instead of the Halacha, as described in Mishna Succah 4:9.) Since no one was allowed to be present in the entire Temple when the Cohen Gadol performed the service in the Holy of Holies (Vayikra 16:17), they could not check up on him. The only recourse was to have him make an oath that he would perform the service according to the tradition. Since even the Sadducees treated oaths as sacred, this was a viable strategy to ensure the service was performed appropriately.

Sefer Daf al Daf raises a clever question based on our Gemara. If one is not bound by an oath made to override a pre-existing Torah obligation, how did the sages expect the suspected Sadducee to be deterred by swearing? He could have easily and correctly rationalized that, according to his beliefs, the oath was null since it overrode his perceived Torah obligation.

One answer given is that if he violates the directive given by the committee of sages, he loses his power as Shaliach to represent the Jews and therefore has no standing, making it not a mitzvah at all. My difficulty with this answer is that, if this were truly operative, there would be no need for an oath because, de facto, he would be entering the Holy of Holies performing a non-sanctioned activity as he did not represent the people. Obviously, he rationalized that his sect represented enough of the people for him to be considered a legitimate Shaliach. Another answer given is that, deep down, the would-be Sadducee is not so sure of his position and therefore is not willing to risk violating an oath. This second answer is fascinating because of its astute assertion regarding psychology and conviction. Often, a person may espouse a particular religious conviction and fool himself to the extent that he truly believes it. He only finds out when he must make a personal sacrifice. This is true for both false and true religious beliefs. Just as this Sadducee was not willing to risk violating an oath on the holiest of days in the holiest of places because he was not absolutely convinced of his position, we too must wonder: which religious beliefs do we espouse but might find hard to sacrifice for? May we never be tested, but if we are, may we find the strength to pass the test.

As a final thought, a simple answer occurs to me. Perhaps the Sadducees have no such tradition that invalidates an oath made contrary to a mitzvah. This is plausible because they did not follow the Oral Torah and took most commandments literally. The Sadducee Cohen might feel that an oath is an oath, no matter what, and therefore feel bound by it. There is a small technical problem with the sages using an artifice and, in a certain sense, buying into the Sadducee’s incorrect belief about oaths. We sometimes find great hesitation on the part of the sages to show any legitimization of incorrect Halacha, especially Sadducee beliefs (see Gittin 56a and Zechariah ben Avkulas’ concern, as well as Mishna Parah 3:7). Nevertheless, I think this is the simplest and most logical explanation.