When I was a part of the Church of Christ, I would feel saved one day (when I did things for God), then the next day I would doubt my salvation (I didn't do enough for God).
So, I tried with all my might to do what was right. I read the Bible constantly, prayed always, went to every meeting of the body of Christ, shared my faith with everyone, studied the Bible with tons of people, led Bible talks, led sermons on Sunday and Thursday night, etc.
Then self-righteousness grew in my heart. I was doing so much for God. Then I looked at those around me. They were not doing anywhere close to as much as I was. Then judgement entered my heart. I started telling others they were going to go to hell because they needed to repent.
In my heart and mind I became a super disciple of Christ. Then one day God humbled me greatly! It really sucked! But I am grateful for it. God taught me the difference between sanctification and justification.
Then I realized there is a sanctifying grace and a justifying grace. It took me a while to realize this, but when I did my self-righteousness and judgement disappeared. I then realized salvation has nothing to do with me and what I do. Instead, it is only what Christ has done that saves us.
Once I realized this, I re-read through the Bible and a floodgate of understanding came upon me. I realized that we are justified by faith in what Jesus has done for us and we are sanctified by the working of the Spirit within us.