What does he mean by, “there will be time to prepare a face to meet the faces that you meet”?

"there will be a time to prepare a face to meet the faces that you meet." Imagine yourself having a conversation with someone close to you, such as your best friend. You both are smiling, laughing, and generally have a good front. Now imagine yourself talking to someone you don't like. The conversation, and you, are very different. You must prepare yourself to meet unkind, hateful people, that's just a part of life.