Jesus wants to address the main struggles his followers will have in his kingdom, and a big struggle will be their relationships with one another. So, Jesus gives us a clear instruction for how we are to deal with our own sin as we also address each others sins.
"Or how can you say to your brother, ‘Let me take the speck out of your eye,’ when there is the log in your own eye? You hypocrite, first take the log out of your own eye, and then you will see clearly to take the speck out of your brother's eye." Matthew 7:4-5