Jesus has commissioned us to remove the specks from other people's eyes. The sins of other people are our concern because we love these people enough to try to keep them from destroying themselves through sin.
However, we are not ready to work on others' eyes until we have first let the Lord deal with our own spiritual blindness due to sin (Lk 6:42). Blind eye surgeons do much more harm than good.
When we repent and confess our sins, we humble ourselves. This is a necessary preparation for dealing with the pride of sin in someone else. Proud preachers turn people off when they call others to humility.
When we repent, we learn several things. We realize the horror of sin, its addictive and paralyzing effects, and most of all the mercy and compassion of our heavenly Father. Without understanding these things, we are not effective in helping others repent. Teachers who don't understand are not very understandable.
Repentance and Confession are essential not only to our relationship with the Lord, but also to our preparation for speck-removal. If you haven't had a plank removed, you're not ready to remove a speck. "Walk the plank" of repentance.