That’s a single statement. The reason you want to be careful with your judgment, is that God will judge you the same way you judge others. This is similar to the petition in the Lord’s Prayer, “forgive us…as we also forgive.”

I’m not sure about the speck/plank parable interacting here, mainly because, as your question shows, it implies that we can “make sure we’re not worse”. But we have sin, too, so we’re definitely not better.

We have to be sure that we’re pointing out sinful behavior and thinking, not perceived character flaws, because we’ve all got plenty of those. Pointing out those sinful things can be done in love, where as pointing out character flaws is usually done out of insecurity.

Without the plank, we can see more clearly, because of the clarity of our own struggle, and we’ll do less damage because of it – imagine trying to get an eyelash out of someone else’s eye while wearing a blindfold.