The correct answer is to compare.
For a reader to compare two or more things, the reader must consider how things are different.
Another option for the sentence could be to contrast. Compare or contrast are equally right,
A good reader needs to understand the different concepts contained in a text. If the reader does not understand the differences it would be difficult for it to have a clear idea and reach a valid conclusion. So, in order to do this, the reader has to compare ideas, propositions, theories or any other element that helps him recognize the differences.