The Zohar writes that whoever retells the story of yetzias Mitzrayim and celebrates it joyfully will be privileged to rejoice with the Shechina in Olam HaBa. The AriZal taught that the Haggada should be recited aloud, with great simcha and focused kavana.
(רעיא מהימנא פ’ בא מ ע”ב, סידור האריז”ל קודם מה נשתנה)
The meshamesh Reb Nachman Maryashin related that when he was once at the Seder of the Rebbe Maharash, and all the chassidim at the table were sitting with awe and derech eretz as they read the Haggada quietly, the Rebbe instructed that the Haggada should be recited aloud.
The Frierdiker Rebbe also read the Haggada aloud, and when he became physically unable to do so, he asked others to do it instead. The Rebbe likewise would motion to the person reading the Haggada to read it aloud. During Hallel, the Rebbe would read aloud with a sweet tune and a noticeable dveikus, tears flowing from his eyes.
(אוצר מנהגי חב"ד ע' קנד, קצח)
One year during the first Seder, Rebbetzin Chaya Mushka, the wife of the Tzemach Tzedek, came running in to the home of her father, the Mitteler Rebbe. While they were performing the Seder at home, her husband had drifted off into a trance of ecstasy, had fallen off his chair, and was lying under the table in a state of klos hanefesh. The Mitteler Rebbe was unfazed and assured her, “Never mind; he will crawl out.”
Rebbetzin Chaya Mushka returned home, only to find her husband in the same position. She ran back to father, who this time instructed some chassidim who had entered to tell the Tzemach Tzedek in his name that he should regain consciousness. They went along with Rebbetzin Chaya Mushka, but as they entered the house, the Tzemach Tzedek stood up and resumed his position at the table.
(למען ידעו ע' 315)
While reciting the Haggada, Reb Levi Yitzchok of Berditchev was filled with tremendous hislahavus. When he reached the words Matzah zu he would become so carried away in dveikus that he would fall from his chair to the floor, overturning the kaira, the matzos and the wine. By the time he came to, the table would be set afresh, and another long white kittel was handed to him to replace the one stained with wine. Putting it on, he would say with visible delight, “Ah! Matzah zu...”
(סיפורי חסידים זוין, מועדים, ע' 367)
