Wherefore, a man being evil cannot do that which is good; neither will he give a good gift.
For behold, a bitter fountain cannot bring forth good water; neither can a good fountain bring forth bitter water; wherefore, a man being a servant of the devil cannot follow Christ; and if he follow Christ he cannot be a servant of the devil.
Wherefore, all things which are good cometh of God; and that which is evil cometh of the devil; for the devil is an enemy unto God, and fighteth against him continually, and inviteth and enticeth to sin, and to do that which is evil continually.
But behold, that which is of God inviteth and enticeth to do good continually; wherefore, every thing which inviteth and enticeth to do good, and to love God, and to serve him, is inspired of God.
(Moroni 7:10-13, The Book of Mormon)
At a point in my life recently I went through a spiritual identity crisis. Am I really a child of God? Is God even there? If God loves me, why can't I feel His love? Am I really a good person, or have I been wasting all of my whole life being good when I could be making other choices that would maybe be more fun? Deep down, without the LDS faith that I was raised in, have my actions been showing the person who I really am? Am I ultimately good or bad? If I'm not sure about God, should I keep living my life the way I have been, or can I loosen up a little and try new things? Will I be happier if I live differently? If I keep living according to the standards I was raised with, will I be lying to myself and others for my whole life and die a hypocrite? Am I wasting my time trying to be good when deep down maybe I'm actually a bad person?
I worried myself sick over these questions. Am I good? Am I bad?
During my confusion, I went on campus one night to hear a special speaker, Elder Jeffrey R. Holland's son David Holland. I don't remember anything about David's speech. But afterward I shook hands with David's father, Elder Holland, an Apostle of the Lord. I expected to just shake his hand and get pushed on through the line. But when our hands met, Elder Holland looked into my eyes and said, "How are you?" I was so surprised by his question, that he'd actually spoken to me, that I just exclaimed quickly, "Good!" He stared straight into my soul, it seemed, with his smoky blue eyes, and replied, "You are good!"
I walked away from Elder Holland in a stunned state. I am good! An Apostle of the Lord told me that I am good. I'm a good person. Elder Holland knows that I am.
I've realized in my life that every time I start to relax my standards, every time I stop doing things I should do or start doing things that I shouldn't do, I'm not as happy, and I feel uncomfortable, and I want to be back where I feel good.
Whether God is there or not and whether He loves me or not, the way I've chosen to live my life brings me satisfaction and it brings happiness to those around me. So how do I know that I'm a good person? The answer is in the verses of scripture I quoted above: if I do good things I'm a good person. If I do evil things I'm an evil person. If I'm serving Christ I can't serve the devil, and if I serve the devil I can't serve Christ.
As a human I have agency. I choose to be good or evil. By choosing good things I choose to be good. Sometimes I slip up and sometimes I doubt, but my life has not been predetermined. I don't need to worry about if deep down, beneath everything that I do, I might actually be an evil person, because if I'm choosing good and doing good then I'm a good person! And that's just how it works, folks.