What does Joshua 22:29 mean?

“Therefore we said, ‘Let’s now prepare to build ourselves an altar, not for burnt offering, nor for sacrifice;

but it will be a witness between us and you, and between our generations after us, that we may perform the service of Yahweh before him with our burnt offerings, with our sacrifices, and with our peace offerings;’ that your children may not tell our children in time to come, ‘You have no portion in Yahweh.’

“Therefore we said, ‘It shall be, when they tell us or our generations this in time to come, that we shall say, “Behold the pattern of Yahweh’s altar, which our fathers made, not for burnt offering, nor for sacrifice; but it is a witness between us and you.”’

When Phinehas the priest, and the princes of the congregation, even the heads of the thousands of Israel that were with him, heard the words that the children of Reuben and the children of Gad and the children of Manasseh spoke, it pleased them well.

Phinehas the son of Eleazar the priest said to the children of Reuben, to the children of Gad, and to the children of Manasseh, “Today we know that Yahweh is among us, because you have not committed this trespass against Yahweh. Now you have delivered the children of Israel out of Yahweh’s hand.”

Phinehas the son of Eleazar the priest, and the princes, returned from the children of Reuben, and from the children of Gad, out of the land of Gilead, to the land of Canaan, to the children of Israel, and brought them word again.