But that it may be a witness between us, and you, and our generations after us, that we might do the service of the LORD before him with our burnt offerings, and with our sacrifices, and with our peace offerings; that your children may not say to our children in time to come, Ye have no part in the LORD.
This verse means that we want a reminder between us and you, and for future generations, showing that we serve the Lord with our burnt offerings, sacrifices, and peace offerings. We don't want your children to tell our children in the future that they don't belong to the Lord.