King James Bible Dictionary

(Heb. kapporeth, a "covering;" LXX. and N.T., hilasterion; Vulg., propitiatorium), the covering or lid of the ark of the covenant (q.v.). It was of acacia wood, overlaid with gold, or perhaps rather a plate of solid gold, 2 1/2 cubits long and 1 1/2 broad (Exodus 25:17; 30:6; 31:7). It is compared to the throne of grace (Hebrews 9:5; Ephesians 2:6). The holy of holies is called the "place of the mercy-seat" (1 Chronicles 28:11- Leviticus 16:2).

It has been conjectured that the censer (thumiaterion, meaning "anything having regard to or employed in the burning of incense") mentioned in Hebrews 9:4 was the "mercy-seat," at which the incense was burned by the high priest on the great day of atonement, and upon or toward which the blood of the goat was sprinkled (Leviticus 16:11-16; comp. Numbers 7:89 and Exodus 25:22).

(Exodus 25:17; 37:6; Hebrews 9:5) This appears to have been merely the lid of the ark of the covenant, not another surface affixed thereto. (It was a solid plate of gold, 2 1/2 cubits (6 1/3 feet) long by 1 1/2 cubits (2 2/3 feet) wide, representing a kind of throne of God, where he would hear prayer and from which he spoke words of comfort.

ED.) It was that whereon the blood of the yearly atonement was sprinkled by the high priest; and in this relation it is doubtful whether the sense of the word in the Hebrew is based on the material fact of its "covering" the ark, or derived from this notion of its reference to the "covering" (i.e. atonement) of sin.