It is indisputable that we all suffer to some extent in our lives. From the standpoint of causality, this means that we have all sinned in our past (including previous lives). The law of causality states that good thoughts and behaviors result in joy, and evil (sin) thoughts and action bring forth suffering.
In some religion, it is important to acknowledge that we have sinned before salvation. In Roman 3:23, it says for all have sinned and fall short of the glory of God. In the Tip of the Writing Brush, it says that we must understand the one truth before understanding God’s innermost heart. This one truth is causality. Suffering comes from our past sins. If we suffer, we have sinned.
The admittance of sin (cause) is important in that we acknowledge that we are not pure in comparison to the innermost heart of God; but it also gives us a starting point where we can turn suffering into joy.
The law of causality reveals why mankind suffers. Until we acknowledge the possibility that we have sinned in the past, we will not be able to understand our sufferings. From this perspective of understanding causality, we have the ability to sweep evil from our minds, and turn the future into joy. Good thoughts and behavior bring forth joy in the future. Understanding causality, gives us an opportunity to turn a new leaf. We all have the potential to have a joyous life with everyone helping each other.