A. The Chassidim are often much more emotional than other groups in their holyday melodies. They usually attach a traditional explanation to each tune.
When, for instance, the Yom Kippur confessions are sung in a bright, happy fashion, they say that this is like the cleaner in a palace who sings at the thought of making the royal floors shine again; similarly, when we confess our sins we feel joyful to be able to cleanse our souls.
On the other hand, on Rosh HaShanah morning Rabbi Aharon of Karlin (18th century) sang HaMelech, “The King”, with such sorrow and sobbing that he could hardly continue.
He later explained that he had thought of the story in the Talmud (Gittin 56a) that when Rabban Yochanan ben Zakkai came before Vespasian he said, “Peace be to you, O king!” and Vespasian replied, “If I am a king, why have you not come to me until now?”
“Hence,” said Rabbi Aharon, “When I began to sing, ‘The King!’ my heart grew sad within me, for God is a King, and why have I left it until now to come before Him in penitence?”