Speaking to LTV, the archbishop said he suspected many people are waiting for the last moment to apply for the event, for which attendees are advised to register in advance either via their church or a special online site.
The archbishop said that while it would be possible to attend Holy Mass without a reservation, it would mean being banished to the periphery rather than being front and center-stage.
The pilgrimage to Aglona events earlier this week served as "a general trial for the Pope's visit," Stankevičs said, and declared them a great success.
Asked about the position of the Catholic Church in relation to serious crimes, including the sexual exploitation of children, Stankevičs replied that Pope Francis had proclaimed "zero tolerance" for clergymen committing crimes.
"The church has moved to clean its ranks from false shepherds," he said, while stressing that not many priests were corrupted.
"The church must set an example, not strive to conceal and hide," said Stankevičs.
Pope Francis will arrive in Latvia on September 24th, which has been declared an official holiday by Saeima.
It will be the first visit to Latvia by a sitting pontiff since Pope John Paul II paid a visit in 1993.