David Rolph Seely (professor of ancient scripture, BYU): 

The ark of the covenant is described in Exodus 25:10–22. It was a chest constructed of acacia wood covered with gold on the inside and the outside. It was three feet, nine inches long and 27 inches wide and high. It was fitted with rings for two poles used to transport it. On the top of the chest was a golden cover called the mercy seat, and two cherubim rested on either side of the cover facing each other. Cherubim were composite creatures that are found in other ancient Near Eastern cultures, in which they functioned as guardians of thrones and sacred places.

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According to the Bible the ark of the covenant had two functions. It was understood as the throne of the Lord, who is described as sitting between the cherubim (see 1 Sam. 4:4; 2 Sam. 6:2). Thus it represented the presence of God and was placed in the Holy of Holies, which could be entered only once a year by the high priest on the Day of Atonement.

 

The ark also served as a repository of the covenant—hence its name—represented by the two stone tablets containing the Ten Commandments. Eventually, according to Deuteronomy, a scroll containing a copy of the law (see Deut. 31:26) was placed beside the ark, as well as a pot of manna (seeEx. 16:33–34) and Aaron’s rod (see Num. 17:1–11). The children of Israel took the ark of the covenant into the promised land, and it was eventually put into the Holy of Holies in Solomon’s Temple in the 10th century BC. It was most likely destroyed when the temple was burned by the Babylonians in 586 BC.

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Each year on the Day of Atonement—Yom Kippur—the high priest took blood from a sacrifice on the altar into the tabernacle. Passing through the veil, the high priest sprinkled the blood onto the mercy seat as a symbol of the reconciliation between God and his people (see Lev. 16).

 

The 16th-century Protestant reformer William Tyndale coined the English word atonement describing the at-one-ment of God and His people in this moment of reconciliation. This word as a noun and as a verb is central to Jewish discussions of the law of Moses and Christian discussions of the redemption of Jesus Christ. It is also a prominent word in the Book of Mormon.

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In the book of Hebrews, chapters 8–9, Jesus and His Atonement are dramatically explained in terms of the high priest at the Day of Atonement, or Yom Kippur. Jesus, as the high priest, brought His own blood as the sacrifice and by sprinkling it on the mercy seat made it possible for all humans to return to the presence of God. Thus the ark of the covenant becomes for Christians a central symbol in the doctrinal understanding of the Atonement of Jesus Christ.