This expression of the soul-side of the human being is brought out by way of his free will choices for Good over Evil. Similarly, the bathroom process has both the quality of clarification and the quality of free will: Clarification—by clarifying that which is healthy from a mixture of healthy and unhealthy; Free will—by having the control and choice when to use this bodily function.
Thus, in addition to the clarification aspect of our role here in this world being paralleled in the bathroom process, the quality of free will that is essential in one's choosing Good from among the Good-Evil mixture of this world is paralleled in the bathroom process by the control one has over one's bodily functions.
Perhaps this also explains why, according to Jewish law, a person is generally not supposed to wait to go to the bathroom when he feels the need to. Just as a zealous person does not put off doing a good deed (i.e., the clarification of Goodness in a world of Good-Evil mixture) when the opportunity presents itself, so too, one is not to put off going to the bathroom (i.e., the clarification of healthy in a healthy-unhealthy mixture) when he feels the need to go.
Ultimately, the bathroom process parallels the world stage that is set for the grand expression of God. When we bless God for giving us this ability to go to the bathroom, we refer to it as a healing since it is something that is painful if we hold it back and we cannot live without. Indeed, it is the basest physical parallel of what our lives are all about.