Repetition is a good teaching method. It is good to repeat yourself more than once in order for the point to be driven home. However, don't repeat something too many times or it may become tiresome. Think of different ways in which you can express the same point. This way it won't seem so monotonous. You can use analogies or activities as different methods in expressing this point.
For example, you could mention how a person may have committed an egregious sin and was judged their entire life for that one shortcoming. Ask them if they have experienced prejudice or judgmental behavior from others for something they have done in their past. One of the main things you could seek to reinforce in the students' minds is to abstain from using judgmental attributes in their day-to-day life.