There is a reason, David prays for God to “Create in me a clean heart, O God, and renew a right spirit within me” (Psalm 51:10), because we are so prone to a critical spirit.
A critical spirit always starts in arrogance. It starts with the belief that I know better. My way is the right way. But as Jeremiah reminds us . . .
“The heart is deceitful above all things, and desperately sick; who can understand it?” 17:9
A critical spirit's purpose is always to deflect from our our own defects. Point the attention towards others’ supposed imperfections and ours stay out of the limelight. But eventually, we will be found out.
“Judge not, that you be not judged. For with the judgment you pronounce you will be judged, and with the measure you use it will be measured to you. Why do you see the speck that is in your brother's eye, but do not notice the log that is in your own eye? 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 7:1-5)
And a critical spirit always results in division. Get enough people focusing on the little things and you can cause a divide that impacts the only big, important thing out there—salvation.
Keeping our heart in check is not an easy task but it is a necessary one as Solomon reminds us when he says, “Keep your heart with all vigilance, for from it flow the springs of life.” Proverbs 4:23