Our own imperfections unfit us for judging fairly
"Do not speak evil of one another, brethren. He who speaks evil of a brother and judges his brother, speaks evil of the law and judges the law." James 4:11
"And why do you look at the mote in your brother's eye, but do not consider the beam in your own eye?" Matthew 7:3
Our own imperfections unfit us for judging fairly. With beams in our own eyes — we cannot see clearly to pick motes out of our brother's eye.
One of the qualities which make us incapable of impartial judgment of others, is envy. There are few of us who can see our neighbor's life, work, and disposition — without some warping and distortion of the picture. Envy has a strange effect on our moral vision. It shows the beautiful things in others, with the beauty dimmed. It shows the blemishes and faults in them, exaggerated.
Then, the lack of personal experience in struggle and pain, makes many people incapable of sympathy with sorely afflicted ones. Those who have never known a care, nor felt the pinching of poverty — cannot understand the experiences of the poor.
Thus in very many ways, we are unfitted to be judges of others.
"Who are you to judge someone else's servant? To his own master he stands or falls." Romans 14:4
"You, then, why do you judge your brother? Or why do you look down on your brother?" Romans 14:10