Halakhah su Isaia 12:8

On the seventh of Pesaḥ, the nights before the holiday, we sanctify it with Kiddush over the wine, and we do not need to say the blessing Sheheḥeyanu over the season. And here ¹ Pesachim 102b:5 is the proof. As it says there: Because Rav did not say that one recites the blessing over the season, learn from that that we are discussing the seventh day of Pesaḥ. Whatever wine he had, he already consumed, and does not have enough for two more cups. And the explanation for this is that the season is included within the pilgrimage. And we pray as on the first two days of Pesaḥ, for the evening and for the morning, but in the Musaf prayer we add to the verses of And you shall present ² Numbers 28:19-24, and we say, And on the seventh day a sacred gathering it will be for you, all laborious work you will not do.³ Numbers 28:25 And its offerings, etc. And we take out two Torah scrolls and read from And it was when he let them go⁴ Exodus 13:17 to For I am the LORD your healer ⁵ Exodus 15:26, since on the seventh day the Israelites of the exodus said the Song at the Sea. And the mafṭir reads from And you shall present to the end of the part⁶ Numbers 28:19-25, and concludes in Samuel, from And there was again fighting in Gath⁷ II Samuel 21:20 to the end of the song of David⁸ II Samuel 22:51, because it is a song, and it has language within it showing similarity to language of the exodus from Egypt, like Smoke went up from His nostrils⁹ II Samuel 22:9 or And he let loose bolts¹⁰ see II Samuel 22:9. And a minor translates it all into the Aramaic translation verse by verse, from And it was when he let them go¹¹ Exodus 13:17 and from the entire song, for this very day Israel crossed the sea, and the section is translated to publicize miracle. And just as it is our custom to translate the Torah into the Aramaic of Onkelos, so too we translate the Prophet into the Aramaic of Jonathan. And we also translate the readings on Atzeret that is to say, Shavuot, but not on the other festivals. On the eighth day we read Every firstborn to the end of the reading¹² Deuteronomy 15:19-16:17, and conclude with Isaiah, at That same day at Nob up to Shout and cheer¹³ Isaiah 10:32-12:6, because the downfall of Sanḥeriv was on Pesaḥ.

“The order at the close of (i.e., after) Yom Kippur” - Containing five paragraphs.
We pray the Evening Prayer²²⁵Arvit, ערבית, the Evening Service; see footnote 144. and say the Havdalah²²⁶Havdalah, הבדלה, literally means distinction. It is a blessing that is recited at the termination of Sabbaths and festivals in order to help distinguish the holy of the holiday from the profane or ordinary nature of the regular weekday. According to the Talmud (Ber. 33a) the men of the Great Synagogue instituted these prayers. At times the prayer was said in the Amidah, but when Israel got richer and could afford it, the prayer was said over a cup of wine and, therefore taken out of the Amidah and placed at the end of the Service. The location of the prayer varied through the tannaitic period. In different rites, different prayers begin the ceremony. Most Ashkenazim recite Isaiah 12:2-3, "Behold, God is my salvation". The introduction is followed by three blessings, over wine, spices, and light, the order varied before it was set down in the Mishna.
The blessing over light was to display that work (lighting fire) was now permitted as the Sabbath or festival was over. The blessing over wine comes from the early established duty to recite the prayer over wine. There is no agreement as to the origin of the blessing over the spices. The rishonim (see footnote 16) state that it is to compensate the Jew for the loss of his "additional soul" which traditionally accompanied him throughout the Sabbath and festivals, although other reasons have also been given.
The actual Havdalah blessing itself, the blessing over the separation of holy from profane, is the fourth blessing in the ceremony. It developed over the years into various versions. It was decided that the prayer must mention at least one distinction, that between holy and profane. When a festival is followed immediately by the Sabbath the distinction mentioned is between the holy and the holy. When a festival is followed by a weekday, Havdalah may be recited over wine alone without the candle and spices. Many local customs developed around this mystical ceremony as did many special songs and hymns.
Editorial Staff, E. J., v. 7, pp. 1481-82. (the “separation”) in the benediction “חונן הדעת²²⁷According to the Sephardi ritual, the Havdalah ceremony was part of the Arvit Service (see footnote 144) and the recitation of the Havdalah was done during the Amidah (see footnote 43). It was inserted into the fourth benediction of the regular nineteen benedictions which make up the weekday Amidah, Ḥonen ha-Da'at, חונן הדעת, a prayer of thanking God for knowledge and understanding.”.