The music in Actraiser matched the action on the screen. The player may have just finished spending a great deal of time building a city and the music helps change the pace of the game.
*Note* I will be speaking a bit about religion in this post. Do not take my writings here as my particular views on religion. I am simply using the game's plot and story and trying to understand what the creators might have been saying.
In the game you play as "The Master" and his angel looking servant. It does not take a giant leap of thought to figure out "The Master" is God and the angel looking thing is an angel. This game was made in Japan where they do not have a problem playing around with Christain theology since it is not their faith. When brought over to America many Japanese games have most of the Christian symbols and plot referring to it removed. Nintendo was especially picky about this since they did not want to offend anyone. However, Actraiser, does a much worse job of hiding its roots. At no point have the Japanese been blasphamous with their depiction of Christianity, it is just that American companies would rather nothing being said about religion at all.