How is offering X Hail Marys not considered vain repetition?

So if the Hail Mary is a prayer and saying the prayer multiple times is **encouraged** in Catholicism, what established reason does the Catholic church give to justify it **not** being a *vain repetition*. > **Matthew 6:7 KJV** But when ye pray, use not vain repetitions, as the heathen do: for they think that they shall be heard for their much speaking. I'm looking for an official Catholic response to this accusation. I'm sure they've said something about it.