It means pay attention to how you judge others because if you do judge other you will be judged yourself and perhaps even harsher. If you are more advanced in your faith then more will be expected of you. For example you can't expect the same of the expert and the amature it's similar in faith. Of course we should all strive to be perfect but God knows that someone who has just started their journey can't do that. It's a reminder to those who are very pious not to become proud with their accomplishments in faith because as they "have more" meaning more spiritual gift, more will be expected of them then of those who are just starting out and who aren't firm in their faith yet.