The idiomatic phrase "make no mistake" is used as emphasis for a statement. It gives the impression that what is being said is firmly true; of course, this is a claim, the opinion of the speaker. Its meaning is that the listener should have no doubt; that the statement should be accepted as true.
Example: "Make no mistake, we will overcome these obstacles and triumph in the end." This is a typical use of the expression. The expression can be applied to any number of causes.