It is not the “words of our mouth” which God is listening to, it is the sincerity and intent of our hearts. Words are helpful physical expressions or symbols of our spiritual intent and sincerity of our hearts, but they are at best limited expressions of what is really happening inside of us.
When we pray. folding arms, bowing head and closing eyes doesn’t make a prayer heard by Father/Mother. But it is a sign and symbol for others that shows what is happening inside us. This is a great tool for teaching children who can’t see the spiritual/inside actions. They can see the outward and so learn about prayer/how to pray inwardly by watching us go through dead motions.
Moroni 7 tells us that praying can be counted against us as evil, i.e. sin if we are praying without real intent. Our intent is our reason. If we are praying because the prophet told us to pray on our meals and when we wake and when we go to bed, then our intent is to follow the prophet and it is counted as evil because praying for any other reason than to sincerely commune with God is considered evil. So, millions of people obey the prophet and pray every day for the reason that “they are supposed to”, and are doing it for the wrong reason and so their prayers remain unanswered and they are counted as evil or sins.