I know the spiritual things I know because God has taught them to me. I have seen his influence in my life as I "counsel with the Lord in all [my] doings" and continually "he will direct [me] for good" (Alma 37:37). God truly shows his love for me by guiding and directing me in ways where I could have never foreseen the outcome, in ways that are far better that my intended path. God has blessed me in this manner so many times, I cannot count them.
I am not a blind follower. I truly know that I know! For "it is a grand thing to know—and to know that you know and that the light has not been borrowed from another" (Douglas L. Callister, Ensign, Nov. 2007). I have been blessed with my own light of truth and knowledge, given to me by God the Father through the Holy Ghost. As I act on this knowledge, it continues to grow and I draw nearer to Jesus Christ.
It is a nearly indescribable feeling to have a testimony independent of any other person that the Church of Jesus Christ of Latter-day Saints is the one true church on this Earth, that God lives, that he is concerned with all things in my life, that Jesus Christ lives again, as a resurrected being after he took my sins upon himself, and died for me that I might have the opportunity to repent, and live with him and God the Father again in their kingdom! I know it is true because I have done as Jesus Christ taught, recorded in the Book of John, I have asked the father in Jesus' name, received an answer that the LDS Church is true, that all these principles I have mentioned and many others are true, and my joy is full (John 16:23-24)!