It was God's idea to arrange the work of the tabernacle to include a special altar for incense. We can be pretty sure he included all that was necessary and nothing that was unnecessary. He offered thanksgiving, he interceded for others, he made petitions. That we, God's children, should be not only permitted but commanded also to come is a mystery. We do not understand.
Spiritual power is released through prayer.
Chances are God won't make my hands clean. That's a job he leaves up to me. His omnipotence is not impaired by his having ordained my participation, whether it be in the washing of hands with soap or the helping of a friend with prayer. Christ redeemed the world by the laying down of his life, a perfect sacrifice, once for all. He lets us participate with him in that business by the laying down of our own lives.