The book covered: Ascent to Felicity translated by Faraz A. Khan, written originally by Abu ‘I-Iklas al-Shurunbulali titled Maraaqi ‘l-Sa’aadat

An important distinction that should be made before beginning is the difference between Wajib (Mandatory) and Fard (Obligatory) within Hanafi Fiqh. Despite their synonymous translations actually contain two different meanings.

We can classify evidence used in rulings underneath four categories:

Definitive Evidence & Definitive Interpretation In-definitive Interpretation & Definitive Evidence
In-definitive Evidence & Definitive InterpretationIn-definitive Interpretation & In-definitive Evidence

To make sense of the four categories I will explain using everyday objects and events.

We have definitive evidence and definitive interpretation that the country of China exists.

We have definitive evidence that humans have dreams, but in-definitive interpretations as to why or how that happens.

We have in-definitive evidence that owning a cat is healthy for the owner, but definitive interpretation that they own a cat and live healthy.

We have in-definitive evidence that playing video games more than 3 hours a day is bad for overall mental health, and and differences of opinion on the meaning of the research conducted.

Now this comes to the conversation of Wajib and Fard.
Fard: Is proven with definitive evidence and definitive interpretation, meaning there is no difference in regards to how it is presented and how it can be understood.

Wajib: Is proven with in-definitive evidence, but definitive interpretation, or definitive evidence but in-definitive interpretation. Meaning that while the interpretation or evidence is there that something may be done, its regards to if it has to be done is inconclusive. Now, here is a caveat in regards to Fiqh. Evidence in this category is generally trustworthy, meaning the evidence in question is not weak or fabricated, but instead that its interpretation is up for debate. In example of this is Witr Salah. From the story of Isra and Miraj we understand that five prayers are mandatory, however, we also have ahadith that describe that RasulAllah SAW stated the necessity of praying Witr. Therefore, because of the level of emphasis placed by the ahadith, it is mandatory. However, because Allah SWT did not state that five prayers were mandatory in the journey and in other ahadith RasulAllah SAW did not state that there were in fact six prayers, it falls into this category. We have definitive evidence that RasulAllah SAW stated that it is mandatory to pray, but its interpretation that is it mandatory is up for debate as other ahadith can present the idea that it is just something so strongly emphasized it should not be missed.

In regards to this as well, it should be noted that abandoning either is a sin. However, abandoning something Wajib will not remove someone form the fold of Islam, whereas abandoning something Fard will. (Last note is that other Madhabs do not have this category and instead use both terms interchangbly.)