At that time the Elder Subhuti arose from his seat in the assembly, uncovered his right shoulder,  placed his right knee on the ground, put his palms together with respect and said to the Buddha…

The ritual performed in requesting dharma symbolizes the purity of the Three Karmas:

1. Uncovering the right shoulder and placing the right knee on the ground represents the purity of body karma.
2. Placing the palms together respectfully represents pure mind karma.
3. Verbalizing the request indicates the karma of the mouth is pure