It was the desire of the eastern tribes that the western tribes come to know the true intention of the altar (Joshua 22:22) and thus realize that the Lord is with us
as opposed to being against us.
There is no need to fear wrath from the Lord because a breach of trust has not taken place.1
31 And Phinehas the son of Eleazar the priest said to the people of Reuben and the people of Gad and the people of Manasseh, “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.”