If your goal is to honestly analyze to then you have to consider the context.

You cited (Numbers 15:32-36) where a man is put to death for working on the sabbath.

From the Biblical timeline we can conclude that this man was likely among the originals who followed Moses out of Egypt. He was thus not only a direct witness to several miracles he heard the voice of God directly at Mt. Sinai.

The problem was that this man was deliberately and flagrantly working in the open on the Sabbath day when God had directly manifested himself and commanded that no work be done on the Sabbath. This was a direct challenge to God's authority.

Apparently, this was the first public offense against the newly revealed law of God. It was, essentially, being tested. Therefore, the severity of the punishment was to demonstrate to all of Israel the necessity of obeying the Law of God.

To further add further context from a Christian tradition we have to consider the following.

Matthew 12:11-12
He said to them, “Which one of you who has a sheep, if it falls into a pit on the Sabbath, will not take hold of it and lift it out? Of how much more value is a man than a sheep! So it is lawful to do good on the Sabbath.”

Mark 2:27-28  
And he said to them, “The Sabbath was made for man, not man for the Sabbath. So the Son of Man is lord even of the Sabbath.”

Combining all of these threads what is the overall message. I think it is a warning. The simple factual based observation that if we fail to strengthen, maintain, and transmit our faith and cultural roots things will go very badly for us..

How much of our time must be dedicated to ensure we succeed in sustaining ourselves and our foundations? Perhaps one seventh especially with regards to the most difficult portion of our duties successfully passing respect for God to the next generation..