The meaning is very plain. We can all understand that knowledge is necessary to make a judgment. In other words he believed that he had given them sufficient information so that they could make a proper judgment. He then instructed his readers to use that knowledge to make a judgment. The judgments may be good or bad, moral or immoral, right or wrong, very knowledgeable or wild guesses, very important or of absolutely no consequence, but judgments we all must make.
Judgment is necessary.
Judging is making a choice. Whether it is the clothing one buys, the house one lives in, the car one drives, a thousand and one other things which constantly come our way, including the moral decisions we make concerning the actions of others, we will all be making judgments. Read verses 1-5 very carefully. Do NOT take the first verse, Judge not that you be not judged , out of its context and give it a meaning totally contrary to the passage. Many people, with glee and smugness, quickly quote that verse when someone says something that they do not like.