The main section of this week's Torah reading describes the revelation at Mt. Sinai and the giving of the Torah to the Jewish people. However, that section is preceded by a multi-faceted narrative dealing with the relations between Yisro, Moshe and the emerging Jewish nation. What is the connection between the two halves of parshas Yisro, and what does it teach us about the main events of the parsha, the revelation at Mt. Sinai and the giving of the Torah?
Rabbi Yitzchak Knoebel, (Sefer Siach Yitzchok) cites Rabbi Ya'akov Kamenetsky who noted that the first part of parshas Yisro is intended to teach us that although the Jewish people are referred to as the chosen nation, this is not a racist notion. Although Judaism is not a proselytizing religion, actively seeking converts, people of other nations, races and religions are welcome to join the Jewish people, as we see in the case of Yisro, following the opinion that he actually converted. This is why, Rabbi Kamenetsky suggests, the account of Yisro's spiritual journey is recorded in the same parsha as the revelation and the giving of the Torah are.
But what was it, that made Yisro so inspired ot Join the Jewish nation. Why separate himself from the greater world showcase and join the former slave nation of Am Yisroel? Rabbi Josh Hoffman (Netvort, 5763) suggests a possibility based on the writings of Rav Kook. According to  Rav Kook's principle, there are two kinds of ethics : mussar enoshi, or natural ethics, and mussar Eloki, or ethics stemming from religion. Religion, writes Rav Kook, must never contradict natural morality, but only build on it and improve. When Yisro's witnessed Moshe's display of gratitude when the latter wanted to leave Midian, it allowed the older man  to go the further step and express his gratitude to God. He began his journey to the Jewish people when he first heard about God's miracles, and was reinforced in his reaction when Moshe again displayed his gratitude by coming out to greet him. Finally, after hearing Moshe's description of the miracles, he went on to express his own gratitude to God in a manner that Moshe himself had not reached.
Rav Hoffman suggests that the same message is being expressed here:  In order to fulfill our role as a 'kingdom of priests and a holy nation," and convince all of mankind of God's sovereignty, as enjoined upon us immediately before the revelation at Siani, we must make sure that we first adhere to the basic demands of moral, ethical living, which include the basic character trait of gratitude to a benefactor. It was this kind of ethical attitude that attracted Yisro to the Jewish people, and serves as an introduction to the Torah's account of the revelation at Sinai.
The Shulchan Aruch (299:10)  notes that one maynot do work before he says Havdala. However, if one said Havdala in Shmoneh Esrai, he may work even prior to reciting the formal Havdala. If work is required even prior to this, he should say Baruch HaMavdil and then do the work. The Rema adds that women who do not regularly daven Maariv should get into the habit of reciting Baruch HaMavdil before they commence performing Melacha. He adds that some note that this is only applicable to actual Melachos (sewing, cooking etc.). However, merely lighting a candle or carrying would be ok.
            The Olas Shabbos notes that according to the Michaber (Shulchan Aruch) no work is permitted before the recitation of HaMavdil because the sanctity of shabbos remains in effect until we remove it through Havdala. The Rema though would argue that the prohibition of performing work is not dependent on the Havdala - the Rabbis wanted us to say Havdala before engaging in real Melacha so as to note the difference between Shabbos and the work of weekdays but actions that are not real work (lighting a match etc.) were not meant to be included.
            The Rambam (Shabbos, 29:5) insists that one not do anything until he recites Havdala with the cup of wine. The Griz (Al HaRambam 29:5) notes that the Rambam means to convey the idea that the title "work' need not be attached to the action. Either way, work may not be done on Motzai Shabbos until Havdala. The Talmud (Berachos 14a) notes that one may not take care of his needs prior to Davening and the Rambam there too, does not stress the idea of Melacha either. Ergo, deduces the Griz, the same must be true with work prior to Havdala where too, the work is not dependent upon the title "melacha" but rather the obligation to recite Havdala.
            The Tur (299) quotes the Rosh (Pesachim 11) and notes that according to the Rosh, one must recite Baruch HaMavdil with a Shem U"Malchus in order for the Beracha to work. The Griz explains that according to the Rosh, one assumes that the prohibition has more to do with the ending of Shabbos than the actual recitation of Havdala as it would seem illogical to establish a complete Beracha just to allow work.
            Hagaon Harav Mordechai Willig Shlita (Kuntres Nachalas Yaakov Ovi, 10) offered a different position and insight into the Tur. According to Rav Willig, the Tur actually agrees with the Rambam that the first tasting of the week should be from the cup of Havdala. Thus, one may not eat prior to Havdala. Parenthetically (according to the Tur), once Havdala has been recited on the cup, one may also commence doing other things. However, one does not need to specifically wait for Havdala Al HaKos in order to work. He merely needs the Beracha of HaMavdil irrespective of whether that Beracha comes with a Beracha on wine or not.
            It should be noted that the Rambam (as interpreted by the Beis Yosef) uses the term Ad SheYavdil and does not ever imply the need to have a cup of wine. He too, according to this position may not require it. The Machatzis HaShekel too (299:17) notes that it is a printer's error to assume that the Rambam requires a full Havdala Al HaKos as the Rambam never mentions the concept of Kos .
            Bottom line, the Shmiras Shabbos K'Hilchasa (59:4:2) entertains the possibility that merely reciting Barchu is akin to a Havdala between Shabbos and weekdays in regard to doing work. There, no full blessing is recited. The prevailing custom is to recite the Havdala in Shmoneh Esrai and/or Baruch HaMavdil without the name of Hashem and to allow work where necessary thereafter but to try to recite Havdala that evening in a timely fashion.
Shabbat Shalom