The Pharisees were very zealous for the Law of Moses, but they also considered themselves the guardians of the oral traditions that scholars developed over generations. The oral traditions interpreted the Law of Moses. For example, the Law said to keep the Sabbath. They were not to work on God’s holy day. Yet, what was work and what was not? The oral traditions filled in the details that Moses left out. For instance, how far could a person walk on the Sabbath without it being work? The interpreters decided that the distance was 2000 cubits which is about 2/3 of a mile. This was known as a Sabbath’s day journey. Where did they get that number? When the Hebrews carried the Ark of the Covenant in the wilderness, God commanded them to walk 2000 cubits behind the ark. They decided that was God’s way of telling them how far one could walk on the Sabbath.
Wow! The GB are trying to fill the same role the Pharisees did. They fill in the rest (e.g. blood components are wrong, but hemoglobin is acceptable).