When I talk to Tenrikyo church members, they believe that the Joyous Service helps them sweep evil thoughts or dusts from their mind. They say that God helps them do this. I find this puzzling, since in the Ofudesaki, God gives us the ingredients to sweep evil from our own minds. God tells us that any illness or obstacle that appear in our lives, we must calm our minds and ponder our own dusts. This is how we purify our own minds. This process is difficult, since we have a tendency to blame others for what appears in our lives. God also tells us that we have control of our own minds, and I would presume that it is up to us to change our way of thinking.
Then who is the prayer directed toward? The following is from the Ofudesaki:
The Service, where do they come from, you think.
Those in high places, they will come spirited. 2-4
We pray to save others. We are asking God to help sweep dusts from others, especially to the people we have spread God’s truth to.
But just by performing the Joyous Service, God will not help us save people. First we need to purify our own minds by the directions given in the Ofudesaki. When our minds are purified, then the Joyous Service becomes effective. The following from the Ofudesaki confims this.
TheJoyous Service to obtain, what makes it effective do not wonder.
The mind’s truth, the Original mind makes it effective. 4-51
This is telling us that we must have a pure mind, like the Original mind given to the first parents of human beings before our prayers are accepted by God.This is why throughout the Ofudesaki, God is telling us God is hastening and preparing the early followers for the performance of the Service. The preparation is not the physical aspects of the Service, like the hand movements and words, but it is the mental prepartion that God is hastening. God is waiting for us to obtain the Original pure mind. Then and only if we perform the Joyous Service, God will begin to help us save others; bringing the world to our places of worship.
Evil sweeping, save THEM please, Tenri-O-mo-Mikoto
All this information is in the Ofudesaki. The most updated translation in the Ofudesaki is at heaventruth.com, and also can be seen daily on Facebook Tenrikyo Ofudesaki Study Group. 
Heaven's Truths, in Healing the Body 