From the Help menu inside of the OmniFocus app:
Originally Posted by elektroglide
anyone know the solution?
Focusing on certain projects or folders
If you know that you want to concentrate for a while on a particular project, folder, or combination of items, the Focus feature can get everything else out of your way.
Select a project or folder (or any combination of projects and folders) in the sidebar.
Click the Focus toolbar button, or choose Focus on (Selected Items) from the View menu. Everything outside your selection disappears from the sidebar, and the title at the top of the window changes to Focusing on (Selected Items). (You can also hold option while double-clicking an item in the sidebar.)
As you work in planning mode, or switch to context mode, OmniFocus ignores everything outside of your focus, as if the items you’re focusing on are the only items in your library.
When you’re done focusing, choose Show All Projects from the View menu, or click the Show All toolbar button. Your library comes back as if nothing ever happened!
When you find yourself using a certain set of contexts, focus, and view bar filters pretty often, you might want to save them as a perspective.