Answer:
At the beginning of the conflict between peasants and the nobility in Germany, Luther played more of a neutral role, trying to get the two sides to see each others' view. As the peasants rose up in power, Luther decided that the peasants should respect their nobles as kids should respect elders.
The peasants thought Luther would side with them during the revolt because he had spent his life's work against the church and not siding with them. He was basically revolting! But no Luther did not side with the peasants, instead he saw them as a threat. I believe this may also be because if he had sided with the peasants and they lost the nobles will not follow him and his new way of viewing the church.
Hope this helps!