Love the sinner; hate your own sin. Judging someone impersonally is assuming God's authority as your own. Yet, praying for someone personally is assuming God's heart as your own. Jesus isn't prohibiting judging in general, but He is raising the standard within our own hearts to make space for God's grace and mercy in ourselves and our relationships. A powerful use of the Golden Rule is to pray God's grace and mercy for the person in the same way Christ has shown his grace and mercy to you.