Bava Kamma 021

1:
Our mishnah seems simple but it is not. The best way to make sense of our mishnah is to quote the Gemara extensively with copious explanations.

2:
The discussion in the Gemara [BK 32a-b] starts of with a note about the identity of Tanna Kamma:

Our mishnah teaches that if one or both of the people using the public domain is running they are both not liable. Issi ben-Yehudah is of the opinion that someone running in the public domain is sufficiently different from the other pedestrians to make him liable for and damage he causes. This being the case, the Gemara determines that Issi ben-Yehudah cannot be the author of our present mishnah.

3:
However, the barayta just quoted now continues:

Even though Issi ben-Yehudah holds that someone running in the public domain is liable for any damage he may cause on most occasions on Fridays at twilight everybody has permission to run in the public domain because they are hurrying to get everything ready for Shabbat.

4:
The Gemara now continues:

Rabbi Yoḥanan is of the opinion that on ordinary occasions the halakhah is that propounded by Issi ben-Yehudah, and not what seems to be propounded in our mishnah: people running in the public domain are liable for damages. This opinion of Rabbi Yoḥanan in itself is strange and the Gemara quickly points this out:

Rabbi Yoḥanan is the sage who propounded the general rule that we have mentioned on many occasions over the years. Some mishnahs, like our present mishnah, do not have attached to the mishnah the name of the sage with whom the ruling originated, so the mishnah remains anonymous. On other occasions we have noted that sometimes there is more than one opinion quoted in a mishnah: the first is anonymous and the others are attributed to various sages. For convenience we call the anonymous sage Tanna Kamma, the First Sage. Rabbi Yoḥanan laid down the rule of interpretation that any mishnah which is anonymous is, in fact, halakhah. So how can Rabbi Yoḥanan hold these two views simultaneously: that halakhah follows an 'anonymous' mishnah but that in our present case halakhah follows the opinion of Issi ben-Yehudah?

5:
The Gemara suggests that the best way to reconcile the two opposing views of Rabbi Yoḥanan is to assume that our present mishnah is elliptic,and that a major clause is missing!

The Gemara here suggests what we call an ukimta: the mishnah must not be understood in a general sense, but it must be understood as referring to certain specific conditions. The sages would have, as it were, our present mishnah read as follows:

6:
By means of this ukimta the Gemara manages to explain our present mishnah and also to propound a general rule:

7:
The Gemara now backtracks to delve more deeply into the opinion of Issi ben-Yehudah (which now has been accepted as halakhah). We learned: "Issi ben-Yehudah agrees that on Fridays at twilight one not liable because he is running with permission." The Gemara now asks about the nature of that "permission".

In other words people are in a hurry on Fridays at twilight because a most important guest is arriving and one must be ready to greet "Shabbat the bride, the queen" the moment she arrives. So people are running this way and that to complete their preparations on time.

8:
This concept of greeting Shabbat on Fridays at twilight was the origin of the custom of the kabbalists of Safed in the 16th century who organized a special ceremony for the occasion. Originally, they would leave town and greet Shabbat in the countryside and then escort her, as it were, into town with dancing and singing. Gradually, the ceremony was moved to the synagogue. Rabbi Yitzḥak Luria, the leader of the Safed Kabbalists, asked Rabbi Moshe Cordovero to work out a special ceremony for Kabbalat Shabbat, greeting Shabbat. He selected six psalms, 95-99 and then Psalm 29. After these they would sing a hymn specially composed by Rabbi Shelomo Alkabetz, Lekha Dodi and the ceremony would conclude with Psalm 92. This greeting of the bride is followed in synagogues to this day.