। ॥ ४१५ ॥
In plain words
Because they are made of the fire-portion, the hands are at home in tending the fire and in worship. Because it is made of the water-portion, the generative organ releases semen and urine.
Close to the Sanskrit
By reason of being a portion of fire, the two hands are intent upon the worship of fire and the rest; by reason of being a portion of water, the generative organ is the performer of the discharge of semen and urine.