As my opinion, the composition could be done by following those ideas:
firstly, ansewer the first question "why do they introduce special days". Well, obviously they can raise people's awareness about those matters by doing that. Besides, that is a good way to motivate those spirit-followers and attract more people to join them.
Secondly, answer the second question "what effects does this have?", It's not difficult too. Nowadays almost everyone know the Children's Day and celebrate it, while some festivals for special workers like the Nurse's Day or the Theacher's Day are also well known. Those festivals represent people's hornor to those workers, and greatly raised their social status.