Here's Why

A new question on Page Ninety Three:  Why must we practice understanding dependent origination? 
Sayadaw answers with an explanation of the seven stages of purification:

Purification of Virtue

Sila (Moral Conduct)
• Precepts (includes Right Speech and Right Action; implies Right Livelihood)
• Guarding the Sense Doors
• Mindfulness and Clear Comprehension
• Being Content with Little (using the requisites with wise reflection)

Purification of Mind

Samadhi (Concentration)
• Abandoning of the Hindrances
• The Jhanas

Purification of View

The Beginning of the 16 Insight Knowledges (Vipassana)
1. Knowledge of the Delineation of Mind and Matter

Purification by Overcoming Doubt

2. Knowledge of Discerning Cause and Condition (includes Cause and Effect, Karma, Dependent Origination)

Purification by Knowledge and Vision of What is Path and Not-Path

3. Knowledge by Comprehension
   Overcoming the 10 Imperfections of Insight (1)
4. Knowledge of Contemplation of Arising and Passing Away (beginning stage)

Purification by Knowledge and Vision of the Way

4. Knowledge of Contemplation of Arising and Passing Away (mature stage)
5. Knowledge of Contemplation of Dissolution
6. Knowledge of Contemplation of Appearance as Terror
7. Knowledge of Contemplation of Danger
8. Knowledge of Contemplation of Disenchantment
9. Knowledge of Desire for Deliverance
10. Knowledge of Contemplation of Reflection
11. Knowledge of Equanimity about Formations
12. Knowledge in Conformity with Truth

Purification by Knowledge and Vision

13. Knowledge of Change of Lineage
14. Knowledge of Path
15. Knowledge of Fruit
16. Knowledge of Reflection 

Sayadaw reminds us that to comprehend the three marks, we must know mentality-materiality and their causes, which are also known as 'formations.'