When summarizing someone in your argument, it's not necessary to include all of their points. Rather, include the points that touch upon your own argument, the points that either support your position or points to which you need to respond.

In addition, be sure that you write a summary that accurately represents your source's point of view--not your own. In fact, that person should say, "Yes, that's what I think." In this way, you will increase your credibility because you will be perceived as fair and objective, which will increase your credibility with your readers.