The 2 answers that apply are:
The events of the story would seem to lead up to the current day.
The shift in tense would clearly separate the two time periods for the reader.
Step-by-step explanation:
The tense is an important factor when writing a story because it helps sequencing the events. If the writer chooses to use simple past at the beginning and the middle and then changes to simple present, it is because the events in the story lead up to the present. It is clear for the readers to separate these two parts of the story, present and past.