Max Weber was hoping that sociology could be a science along the lines of the hard sciences like physics and biology. Because of this, he hoped that sociology could get as close as possible to being objective. In other words, he wanted people to do research objectively rather than letting their results be dictated by what they believed should be true.
In order to achieve this, he said that it was okay for researchers to pick their topics based on their beliefs or interests, but once they started researching, they should leave their values behind and just seek objective truth. They should not use their values to decide, for example, what data to leave in or out of their studies or what conclusions to draw from the data.