judgement

I was going thru the first part of a study about Rahab today that was focusing on forgiveness and judging others- which makes total sense when talking about Rahab. But I find myself trying to rationalize my thought processes which usually means that I'm not totally accepting what I was studying.
I do not have any problems with forgiveness and I love reading about. Being reminded of how much God loves us and has forgiven us when we ask it of Him. That Jesus was willing to die for all of us as a sacrifice and God is always there to pick up broken pieces and mold us back into the shape he desired for us to be in the first place. It's so beautiful the forgiveness that is bestowed upon us. Then knowing that once we are forgiven we are called to forgive others and not hold their past's or their choices against them. Of course that part is harder but it can also bring about so much peace.
Then came judgement and I must admit that I don't particularly like the way that the author went about this section. She initiates the section by saying "According to the following verses, how can we push past our prejudices- our 'prejudgement'- of people and see them simply as sinners saved by grace, just as we are?" After which she proceeds to list these verses: John 13:33-34, Ephesians 4:32, Colossians 3:13-15, and 1 Peter 3:8. All of those verses tell us that we are not to judge each other but to love, show compassion, forgive each each other, and live in harmony. Which is awesome but how does that help a person to now judge? What does it really mean to judge a person? I have a lot of judgements about the people that are in my life and even the people that I meet every day and some of them are not very nice judgements. But that does not really stop me from working well with that person, or hanging out with that person, or "loving" that person - I just still, in my brain, think they are slow, or egotictical, or lazy, or arrogant, or whatever the judgement is that I have about them. Sometimes judgements are based on watching a habitual behavior from a single person. Is that a bad thing?
How is a judgement different than an opinion? They seem to be rather interchangeable. Or does it only become a judgement when you hold something against the person, or place a limitation on what you believe they can do b/c of the opinion that you have formed? Which makes a judgement an act upon opinion.
Then again, maybe I'm way out in left field and thinking about something that doesn't need to be thought about so much