When you are preparing to leave on your mission, you are asked to create a Mormon.org profile. One of the questions that I was asked, was why I was a Mormon.
I put a lot of time and thought into this answer and when I finished it, I felt that it was not just and answer but also my testimony.
So, I am going to paste a version of my answer (there was a word limit) here.
Why am I a Mormon? (why do I believe?)
Let me tell you.
Because of the immense peace and comfort I receive from living the Gospel, and really living it every second of my life. The knowledge that I have an all great and powerful being who loves me. Personally. And has shown it through all the many blessings he has given me.
Because of the guidelines that are given to us. Many see them as rules and restrictions, but I see them as things that set me free to live life without concern for negative consequences. Through these guidelines I completely avoid the situations that would result in sorrow and guilt.
Because of the atonement of Christ that allows for forgiveness when I do stray and I fall short. The true promise that NO ONE is out of His reach of forgiveness. NOTHING is so bad that He will not help and comfort you. Because of His hand that is always extended to us NO MATTER WHAT.
Because this Gospel encourages questions and one finding answers for themselves. The fact that anyone can read the scriptures and interpret them for themselves, and receive personal revelation for themselves. They are expected to NOT follow blindly.
Because it teaches the true principle that God has a plan for everyone of us. He loves us all so much and wants every last one of us to return home to him, there is no way he left us here to figure things out on our own. He has provided us with all the tools that we need to make it back to him.
Because of the trials. As weird as it sounds, the trials that God allows to come to us, as bad and as hard as they may be, they are for our own growth and to make us stronger. We came to this earth to experience hardships and temptation to learn and to grow. I don't want to be the same person I was five years ago. I want to be better and become stronger so that I can return to live with God and help as many others return as I can.
Because of the family unit God sent us to earth with to support and be supported by, and that we can have our families forever.
Because of the people I meet and learn to love despite differences.
I know that Mormons are not perfect, but God, Christ, and their Gospel are and that is why I am a Mormon and know this Gospel to be the truth!