Everything can be changes because change is the only thing thats permanent. Understanding these 2 important points: 1) emotions are energy, 2) energy can neither be created nor destroyed, 3) it can be transformed from one form to another, 4) conclusion – sadness energy can be turned to something positive, i.e negative emotions can be turned to positive emotions. 

Darkness means ignorance and ignorance could be in any sphere of life. Eg: relationships, career related, money related etc. Light is wisdom. Moving away from darkness is acquiring wisdom.

Yes, there exists a world with opportunities. Unlearn what we have been learning all this while and keeping ourselves open to new school of thoughts.

Pain/ sufferings can be in the physical realm (physical body) but the origin of pain can be emotional, mental or even spiritual. Understanding the cause can reduce or address the effect (pain).