We are to compare their outward actions and attitudes to the Word of God. If they conform to the Word of God, they deserve praise. If they violated the clear teaching of the world of God, then we are to take proper action according to the word of God. Then proper action is to be taken when needed according to the word of God. On the other hand, the Christian is commanded not to go beyond the word of God.
Sinful judgment subjects the common, everyday actions of others to our own personal standards.
The Lord is condemning unjust judgment against people because their actions to not pass our personal standards ortraditions we hold dear. The actions of others which we might find disagreeable, no matter who the person is, do not give Scriptural right to speak evil against that person. On the other hand, if we are kind and generous toward others, we will receive kindness and generosity toward us. Both Paul and the Lord Jesus condemn judging in others what we are unwilling or unable to deal with in ourselves. But we are sure that the judgment of God is according to truth against them which commit such things.