Because God comes out of our heart in the form of speech, we must try to make our speech as pure and clean as possible. God is also in the form of Truth. So whatever we will be saying will have an echo: "Let it be so!"
There is a small story for this.
A traveller was going on his way. After going some distance, he was tired on account of the summer heat. By the side of the path there was a big tree and he went there to take rest under the shade of the tree. When he went into that cool shade, he was overjoyed. Then he said to himself, "I am able to find a very cool place; how fortunate will I be if I will be able to get a glass of cool water also here?" Instantaneously, a tumbler of water came down. After he drank that water he thought, "Now I have quenched my thirst, how happy will I be if there is a good bed here because this floor is hard and rough". At once a big soft bed came down. He then thought, "Even in my house, I do not possess such a pillow. If my wife comes here and sees, how happy will she feel?" Immediately the wife also came. He saw here and he thought, "Is she my wife or is she a demon? Will she eat me?" No sooner he said this, she ate him. The tree under the shade of which he sat is 'Kalpavriksha'. In Indian mythology, Kalpavriksha is said to be a tree that fulfills all desires. When the traveller sat under the Kalpavriksha, whatever good things he thought of, he got them instantly. But when he thought about bad things, bad things also came to him. This world is part of Kalpavriksha. We are sitting under the shade of this Kalpavriksha. If we think badly, bad happens to us and if we think in a good manner, good happens to us.
Moral: When our thoughts, our contemplation, and our deeds are pure, the Kalpavriksha of the world will be giving the good things desired by us. Both good and bad will come only from our heart. They never come from outside. That is why in the beginning we have to make our heart as pure as possible.