Why Scripture is Powerful

But the book shall be delivered unto a man, and he shall deliver the words of the book, which are the words of those who have slumbered in the dust, and he shall deliver these words unto another; But the words which are sealed he shall not deliver, neither shall he deliver the book. For the book shall be sealed by the power of God, and the revelation which was sealed shall be kept in the book until the own due time of the Lord, that they may come forth; for behold, they reveal all things from the foundation of the world unto the end thereof. And the day cometh that the words of the book which were sealed shall be read upon the house tops; and they shall be read by the power of Christ; and all things shall be revealed unto the children of men which ever have been among the children of men, and which ever will be even unto the end of the earth. - 2 Nephi 27:9-11

Some departed prophet and seer of your own island has left, tattooed round the circumference of your flesh, a spiraling revelation, a promise of forgiveness, a complete theory of repentance, a mystical treatise on the art of attaining truth, a riddle in your own proper person to unfold, a messianic text inscribed in your flesh. This prophet came and went long before you arrived.The tattoos are meant for you; they are a kind of story of your life inscribed within your life, but—here’s the trick—you're going to have to die young in order to read them. Order your coffin, lay the length of it and let your life end, die to this world, and then remember that you've forgotten to wash a dish or kiss your wife or sweep the porch or read to your child.Then leap from your coffin and return in earnest to the work of washing and kissing and sweeping and reading, sure and fearless in the time that remains. - Adam S. Miller, Early-Onset Postmortality

Do ye not remember that I said unto you that after ye had received the Holy Ghost ye could speak with the tongue of angels? And now, how could ye speak with the tongue of angels save it were by the Holy Ghost? Angels speak by the power of the Holy Ghost; wherefore, they speak the words of Christ. Wherefore, I said unto you, feast upon the words of Christ; for behold, the words of Christ will tell you all things what ye should do. - 2 Nephi 32:2-3

When you read scripture, you're reading the thoughts of God.  That is, you're reading the thoughts of people who - because they were close to God - were able to say that (at certain moments) His thoughts were their thoughts. By writing these thoughts down, they channeled divine light into a fixed form that, instead of dulling it, gives it the unique quality that makes that work of scripture needed. Works of scripture are different because people are different.

And yes, that does mean that people outside the Church can write scripture. The Bhagavad Gita is a very powerful divine work in this way. So is, funnily enough, Beelzebub's Tales to His Grandson. The Qur'an goes without saying. These differ from each other in what they teach. However, both Swedenborg and Steiner say that thoughts do not remain after death. What makes Islam, Hinduism, and Christianity distinct disappears in the other life, though that does not mean that Muslims stop being Muslims or Christians stop being Christians. To use a metaphor: the cakes have been made, so we no longer need the molds that made them differently shaped. But though they may have a different "timbre," the brightness in each is the same.

This brightness is divinity itself. As such, it is your divine nature. Ever wonder why, when reading the Book of Mormon, you can learn about your own life in a way you can't elsewhere? It's because your divine nature, your heart of hearts, is laid up for you in the book. It is the "sealed portion" to come forth. It's what "retains its brightness."

As such, when you read scripture, you become aware of the spiritual center of your being. Moreover, you become aware of the spiritual center of the world's being. By receiving the brightness of God,  you start to see things from His perspective. You wake up from the sleep of the natural man and, like a contagion, spread that wakefulness to everything else that has forgotten its divine nature.