Managers who read the executive summary should get the essence of the project status without the need to get into the fine details.
For example, if a company performs a competitor analysis prior to deciding whether or not to move in different strategic direction, a business plan would be put together to articulate findings and suggest next steps.
This business plan would open with an executive summary.
The most straightforward way to do this is to create a business plan that includes all of your research, findings, and suggestions.
This business plan naturally requires an executive summary.