God made a covenant (a conditional covenant) with the children of Israel through His servant Moses. He promised good to them and their children for generations if they obeyed Him and His laws; but He always warned of despair, punishment, and dispersion if they were to disobey. As a sign of His covenant He had the Israelites make a box according to His own design, in which to place the stone tablets containing the Ten Commandments. This box, or chest, was called an “ark” and was made of acacia wood overlaid with gold. The Ark was to be housed in the inner sanctum of the tabernacle in the desert and eventually in the Temple when it was built in Jerusalem. This chest is known as the Ark of the Covenant.
The real significance of the Ark of the Covenant was what took place involving the lid of the box, known as the "Mercy Seat." The term ‘mercy seat’ comes from a Hebrew word meaning “to cover, placate, appease, cleanse, cancel or make atonement for.” It was here that the high priest, only once a year (Leviticus 16), entered the Holy of Holies where the Ark was kept and atoned for his sins and the sins of the Israelites. The priest sprinkled blood of a sacrificed animal onto the Mercy Seat to appease the wrath and anger of God for past sins committed. This was the only place in the world where this atonement could take place.
The Mercy Seat on the Ark was a symbolic foreshadowing of the ultimate sacrifice for all sin—the blood of Christ shed on the cross for the remission of sins. The Apostle Paul, a former Pharisee and one familiar with the Old Testament, knew this concept quite well when he wrote about Christ being our covering for sin in Romans 3:24-25: "…and are justified by his grace as a gift, through the redemption that is in Christ Jesus, whom God put forward as a propitiation by his blood, to be received by faith." Just as there was only one place for atonement of sins in the Old Testament—the Mercy Seat of the Ark of the Covenant—so there is also only one place for atonement in the New Testament and current times—the cross of Jesus Christ. As Christians, we no longer look to the Ark but to the Lord Jesus Himself as the propitiation and atonement for our sins.