Learn Farsi: ایشان دکتر هستند و فردا تشریف می‌برند. - He is the doctor and he is leaving tomorrow.

In Farsi, you can use the third-person plural pronoun ایشان to refer to a single person when you want to show them respect. This is very common when talking about esteemed individuals like doctors. Because we used a plural pronoun, the verbs in the sentence must also take plural endings.

Since we are only talking about one doctor, why do we use هستند instead of است?

Grammatical agreement always follows the form of the pronoun, not the literal number of people. Even when ایشان refers to one person deferentially, it remains grammatically plural. Therefore, you must use the plural verb هستند rather than the singular است.

What does تشریف می‌برند literally mean here?

The noun تشریف refers to honor or presence. The compound verb تشریف بردن literally means to take one's honor somewhere, which is a highly polite, deferential way to say to go or to leave. It is the respectful counterpart to the ordinary verb رفتن.

How would this sentence change if I were talking informally about a close friend who happens to be a doctor?

For a close friend, you would drop the formal respect system and use singular forms. ایشان would become او, هستند would become است, and you would use the standard verb for going, making the informal sentence او دکتر است و فردا می‌رود.