The Mercy Seat is the cover of the Ark of the Covenant which was made out of solid gold. In the original Hebrew, this part of the Ark was called ‘Kapporet’ {כפורת} which literally means ‘covering.’
The concept of ‘covering’ in Biblical Hebrew can be understood also in an abstract way as ‘covering sins’ – meaning ‘to grant atonement’. Precisely as the English name for the holiest day in the Jewish calendar – ‘ Day of Atonement’ which in Hebrew called ‘Yom Kippur.’ {יום כיפור}
Yom Kippur {יום כיפור}shares the same Hebrew root as the word ‘Kapporet’. {כפורת} Both of these Hebrew words are strongly connected not just grammatically. The Ark of the Covenant was placed in the holiest place in the Temple –’Holy of Holies’ which was strictly forbidden to enter except for by the High Priest and only on the holiest day in the Jewish calendar – ‘Yom Kippur’.