What does this quote mean Let the end be legitimate let it be within the scope of the constitution and all means which are appropriate which are plainly adapted to that end which are not prohibited bu?

Let the end be legitimate, let it be within the scope of the constitution, and all means which are appropriate, which are plainly adapted to that end, which are not prohibited, but consist with the letter and spirit of the constitution, are constitutional.

It's a reference to the necessary and proper clause where Congress can pass legislation in areas that aren't specifically enumerated in the Constitution, but are necessary to facilitate one of the areas that is enumerated. What Marshall is saying in this quote is that the "end" (i.e. the enumerated power of Congress) must actually be a legitimate power--nothing arbitrary. The "means" (i.e. the legislation they pass to aid the "end") must be appropriate to obtain the end and not be contrary to any other section of the Constitution.