A person must serve God with trepidation and fear, as though he were standing before a king.
This point of contemplation is the starting point at which a Jew must begin his thoughts, meaning that this is how a person views his situation.
He is not like someone sitting in an inner room and doing something which will have an effect elsewhere.
He is performing his divine service now.
He is standing before the King.
The King is present here and now, and is watching him.
The emotional result of this contemplation of serving God with trepidation and fear is that he actually feels trepidation and fear, triggered by the thought that he is standing before the King.
Rabbi Adin Steinsaltz