For a reader to (blank) two or more things, the reader must consider how the things are different.

For a reader to contrast or compare two or more things, the reader must consider how the things are different.

It is an obvious thing when you are going to contrast or compare two things, you must see the things one by one to find the difference between them, this is the important to read or study about the things individually to find the difference. when you know about them, you can compare easily.