# their brothers, their nobles

"their fellow brothers the nobles". These phrases refer to the same people.

# bound themselves with both a curse and an oath

"they took an oath and called for a curse to come on themselves if they failed to keep it"

# to walk in God's law

"to live by God's law" or "to obey God's law"

# which was given by Moses the servant of God

"which Moses the servant of God had given to Israel"

# to observe

"to follow"