Why the writer arrived at one hundred and no more or less, is hard to tell. I am not at all sure that all the items mentioned can be classed as sins. The tract includes a multiplication of requirements and an appeal to all kinds of rules and regulations. We should distinguish between rules and principles. Rules change, and vary in different parts of the world, in different countries and situations.
Principles never change.
They are eternally binding. When every infraction of a rule is treated as a serious violation of a principle, religion increasingly creates guilt, anxiety, and condemnation. People cannot live with that, not for long. The cold morality of rules tends to become undiscriminating and heartless. We tend to become suspicious of people and neglect our responsibility as loving Christians.