I have some questions that have been troubling my mind that I hope you will treat seriously. When I pray vocally I assume that Satan could hear my prayers and attemp to insert his “answer.” Am I correct in this assumption? My next question is this: When I pray silently can Satan “hear” my prayer? Can he know my thoughts at any time?
It is true that Satan cannot enter our minds and read our thoughts. We read in Mormon scripture the Doctrine and Covenants 6:16 that
there is none else save God that knowest thy thoughts and the intent of thy heart.
However, in D&C 19:28 we are commanded to pray vocally–
And again, I command thee that thou shalt pray vocally as well as in thy heart; yea, before the world as well as in secret, in public as well as in private.
The ability to overcome the influence of the Adversary does not lie in hiding from him that which we attempt to do, but we may limit his power by living in such a way that he cannot influence either our thoughts or our actions. Helaman in th Book of Mormon taught his sons, Nephi and Lehi, the following–
And now, my sons, remember, remember that it is upon the rock of our Redeemer, who is Christ, the Son of God, that ye must build your foundation; that when the devil shall send forth his mighty winds, yea, his shafts in the whirlwind, yea, when all his hail and his mighty storm shall beat upon you, it shall have no power over you to drag you down to the gulf of misery and endless wo, because of the rock upon which ye are built, which is a sure foundation, a foundation whereon if men build they cannot fall (Helaman 5:12).
Do not fear the Adversary. Fear only God, such that you would never displease Him. If you do that, Satan can have no power over you.