Why was the Ark of God important?

The Ark reminded God's people that God was with them.

The Ark of the Covenant was a symbol of God’s presence with the people. As priests in Israel, Eli’s sons were responsible for leading the nation in worship of the one true God. Part of their responsibility would have been seeking God’s guidance on going into battle. Instead of seeking God’s direction, Eli’s sons took it upon themselves to send the Ark into the battle. God’s presence was always with the nation of Israel. The Ark symbolized God’s dwelling with and among His people. The Israelites mistakenly thought that if they had the Ark with them in battle, God would be there to fight for them. As a result of their sin, the Ark was captured by the enemy.  Eli’s sons and many other Israelites were killed in battle. As the Ark in the Old Testament symbolized God’s presence with the people, God gave His people something much greater than a sign: He sent His Son, Jesus.