He (falsely) promised to King Charlemagne that he will become a Christian if the Emperor leaves Spain. But Charlemagne did not trust nor believe him so he decided that an envoy must go to King Marsillion to make sure if the promise was true.
Later, the lion is netted by hunters. Hearing it roaring, the mouse remembers its clemency and frees it by gnawing through the ropes. The moral of the story is that mercy brings its reward and that there is no being so small that it cannot help a greater.
no its supposed to be
what was the message of emperor charlemagne to king marsilion
the answer is emperor charlemagne told king marsilion if he surrenders he will convert him to christian