Because this was the [[zava'ah ]] of your [[Rebbe]]! If you don't do it he will not recognize you at the resurrection.
What is the symbolism in the blessing over wine the [[Kos shel Brakha]] after Sabbath[[Seuda Shlishit]] for [[Havdalah]] on [[Motzei Shabbat]]?
Your Rebbe has decreed for you that this blessing is to be regarded as the toast of the [[Brit Chadasha ]] for the sake of which he made [[Kiddush haShemHaShem]]. Anyone who makes this toast is in the Brit Chadasha. The sages taught us that the blessing over the cup Kos for Havdalah is guaranteed to merit you a place in [[Olam HaBa]]. It is the substitute for Thanksgiving Hoda'ah offerings in the Temple Beit HaMikdash according to the Brit Chadasha.
It means as long as you give thanks for the Sabbath Shabbat then you are in the new Covenant Brit Chadasha and your sins will be forgiven as (you are merited a place in the world to come).
Remember when you say [[ata chonantanu ]] or [[bein kodesh lekol Sabbath ]] then Shabbat is over and we are in the [[Motzei Sabbath FastShabbat Tzom]]. And when one finishes saying Havdalah over the Kos shel bracha and drinks, the Motzei Sabbath fast Tzom is over!
So why instead of rushing to eat other food you should eat the [[shirayim ]] and dregs from Sabbath instead?
This is to say to yourselves that you do not chase after the world but we miss the time we spent with the Lord and even though you are now free to pursue other things the first thing we do is try to grab hold of the remnants of Sabbath instead, thereby baring witness that you are not of this world but belong in the Sabbath rest.
That is why you should want the shirayim after Sabbath and the blessing over the cup is finished. Because you are immediately putting yourselves in the mode of longing for the Sabbath.
```To long for the Sabbath Shabbat is Yesod```, the flesh of the son of Man and true body of all who do the will of God and finish his work. How? Because if you "long for Sabbath all week " (placing shirayin a Jewish monstrance) it will help you prepare better for the coming Sabbath and will encourage you to do positive mitzvot!
And if you say Havdalah to sanctify the end of the Sabbath with thanksgiving your offering is accepted and your sins in neglecting the negative mitzvot are forgiven.
This is how to be a Messianic Noahite according to Hassidean Romaniote minhag.
