In His Sermon on the Mount, Jesus tells his followers, “When ye pray, use not vain repetitions as the heathen do: for they think that they shall be heard for their much speaking” (Matthew 6:7).
The Savior is making at least two points. One, your prayers don’t need to be long and full of words. Heavenly Father doesn’t decide which prayers to answer based on who talked the longest.
Two, even if your prayers are short and to the point, be careful not to use “vain repetitions.”
But what does that mean? Does it mean not using the same words every time you pray? Not necessarily. For example, there are only so many different ways to say “I’m grateful for my family.” Using the same words every time you express your gratitude doesn’t mean your gratitude isn’t real.
But the risk of falling into habits in our prayers is that we might start saying the usual things without really thinking about them. When you become a sort of prayer robot, that’s when repetition becomes “vain”—pointless, of no use. Jesus isn’t saying you need to get out a thesaurus every time you pray to make sure you’re varying your language. He just wants you to mean what you say. He wants you to be thoughtful when you talk to Heavenly Father.
One last point: The sacrament prayers are the same every time. What keeps them from being “vain repetitions” is that they are the words of a priesthood ordinance like baptism. That’s something to keep in mind if you’re the one blessing the sacrament.