Two answers that were given here:

(a) The Gemara later (55a) says that if one refrains from reading the Torah when he is called upon to read, this "shortens one's days and years." If he prepares the Parshah two times, he becomes sufficiently familiar with the words and is able to read from the Torah in the event that he is called upon. He thereby avoids having his days and years shortened, and he merits long life. (RAV ELAZAR MOSHE HOROWITZ)

(b) One who disciplines himself and arranges his schedule in order to ensure that he has time to read the Parshah twice and its Targum once each week shows that he appreciates the value of time and uses it productively. He is granted more time in this world to learn Torah and do Mitzvos. (-As heard from Rav Kalman Weinreb, shlit'a.)

Two answers that were given here:

(a) The Gemara later on (Berachos 55a) says that if one refrains from reading the Torah when he is called upon to read, this "shortens one's days and years." If he prepares the Parshah two times, he becomes sufficiently familiar with the words and is able to read from the Torah in the event that he is called upon. He thereby avoids having his days and years shortened, and he merits long life. (Rav Elazar Moshe Horowitz)

(b) One who disciplines himself and arranges his schedule in order to ensure that he has time to read the Parshah twice and its Targum once each week shows that he appreciates the value of time and uses it productively. He is granted more time in this world to learn Torah and do Mitzvos. (-As heard from Rav Kalman Weinreb shlit'a.)