The goal of the passage study process is the single sentence summary that distills the message of the passage into a short statement. This sentence then acts as sheriff of the sermon preparation process, determining whether each element of the message should be there or not. The sermon is all about the effective delivery of the main idea.
If you have thirty seconds to preach, then the main idea is the message. Given the bonus of two more minutes, then you can give an overview of the text to support the main idea. Given the frivolous extravagance of an extra thirty or forty minutes, you can develop every element of the structure in order to drive home the main idea as effectively as possible.
In the message preparation process you begin with one concise, pregnant sentence. As you move through the process, the message grows and develops.
My wife has been pregnant four times. Each time it is exciting to consider the growth of the child inside. Now it is too small to see, now it is the size of a peanut, the size of a strawberry, like your fist, the size of your outstretched hand, etc. When that baby is born it seems so tiny, but then it grows and grows. All the necessary information for that unique individual is contained in the individual imperceptible cell at the beginning of the journey.
The same is true of a message. The short, pregnant sentence of the message idea is ready to grow and develop into the message. So no time spent on the formulation of that sentence is wasted. Rather it is an investment in the message to come, with all its uniqueness and biblical potency.