Joshua 22 tells the story about the Altar of Witness built by the Eastern Tribes of Israel.
When they came to Jordan in the land of Canaan, the people of Reuben, Gad, and the half-tribe of Manasseh built a huge altar. The other tribes of Israel got word that they had built the altar, and the whole assembly of the people gathered at Shiloh for war.
They thought the altar was made in rebellion of Yahweh. They reminded the people of the wrath and destruction from the Lord for serving false gods, and pleaded with them to serve God instead of baal.
But the people of Rueben, Gad, and Manasseh answered that the One True God knew their hearts, and they were not turning away from God. They did not build the altar for burnt offering, or sacrifice, but for a witness between them and God, and for future generations after them. It was built to be a witness that they serve the One True God.
When the priest and chiefs of the congregation heard this, they knew their hearts were pure. Phinehas, son of Eleazar the priest, told the people of Reuben, Gad, and Manassah, "Today we know that the Lord is in our midst, because you have not committed this breach of faith against the Lord. Now you have delivered the people of Israel from the hand of the Lord."
The People of Rueben and Gad called the altar "Witness." They said, "It is a witness between us that the Lord is God!"
As Christians, we should ask ourselves: Are we a witness before God? Do we stand before God and men as a living witness that God is real? When others rise against us thinking evil, are we founded in God's Word to give them assurance that we serve the One True God?