I am really impressed with this simple (not "simplistic") explanation of the necessity of both theory and practice as inherent parts of an effective revolutionary strategy. Although directed to a British audience, most all of it applies to the US except for some details.
In the midst of a discussion of mainstream economics in Capital, Marx comments, ‘all science would be superfluous if the outward appearance and the essence of things directly coincided‘. In other words things are normally not as they appear on the surface or in our immediate experience. This is why we need theory.
Capitalism in particular works in a way that conceals its own dynamics.