According to some traditional interpretations of the Book of Exodus, Book of Numbers, and the Letter to the Hebrews, the Ark also contained Aaron’s rod, a jar of manna, and the first Torah scroll as written by Moses; however, the first of the Books of Kings says that at the time of King Solomon, the Ark contained only the two Tablets of the Law.
According to the Book of Exodus, the Ark was built at the command of God, in accordance with the instructions given to Moses on Mount Sinai. God was said to have communicated with Moses “from between the two cherubim” on the Ark’s cover. Read More here.
God made 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.
The real significance of the Ark of the Covenant was what took place involving the lid of the box, known as the “Mercy Seat.” 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. Read more here.