This is how I know.
I was raised attending a fundamental Baptist church in east Texas. Every Sunday our preacher's sermon was about accepting Jesus as savior or go to hell. I heard about sin, hell, Jesus dying on the cross, and “believing” in Jesus. At age 13 we had a week long revival and at the end of each of his sermons the visiting preacher would walk up and down the aisle begging people to go to the altar to accept Jesus as their savior. At the first service I remember thinking to myself “I hope he doesn't come over to me.” Well, he did, and when he put his hand on my shoulder, I found myself walking down the aisle to the altar. I was met by my SS teacher at the altar, and he asked me if I wanted to accept Jesus as my savior. Of course, I said “yes” so he had me repeat a prayer after him. I was told that I was now “saved,” and the next Sunday I was baptized in the regular church service.
By the time I was about 17-18 years old I wasn't sure if anything I had heard in church was true. I didn't care anything about going to church; I forgot about God and did things teenagers do. Later I finished high school, went to college & graduated not knowing what kind of job/career I should pursue, and finally settled into a teaching career as a math teacher, got married and started thinking about things young married couples think about.
By the time I was about 25-26 years old I stated to question myself about thinking that God was not real. I had serious doubts about all the stuff I had been taught in church as a kid being true. I wasn't convinced that the bible was true or that God existed. I did not understand how “believing in Jesus,” if he WAS real, would save anyone, and I did not understand how saying a prayer “in Jesus' name would save anyone. None of it made sense to me and I just did not get it. But, although I did not “get it,” and I wasn't convinced that any of it was true, for some reason I began to think a lot about what would happen to me if I was wrong, and the bible is true.
After several miserable years of doubting the truth of the bible, I started going to the church that I grew up in and pretend to be a Christian. Deep down inside I knew that I seriously doubted that I was a true “believer,” and many times I would try to work up a sense of “belief” then say a prayer asking God to save me. Afterwards I would have peace for maybe a day, but then the doubts would come back and again the fear & misery took hold of my life. The “believe in Jesus” part was the main thing that had me confused; I did not understand the meaning of “believe.” I began to ask people at church a lot of questions about the bible & about believing in Jesus. I still wasn't sure if any of it was true, but I wanted to know one way or the other. I talked to our SS teacher, the preacher, and other Christians. None of them could give me any answers that convinced me of the truth of the bible. No one could explain to me how saying a prayer in Jesus' name would save anyone. No one could convince me what was meant by “believing in Jesus.” I was still as confused as ever and did not know what to do about the matter. I found some books in the church library written by well known Christians authors, and I read those books over & over. Those books only repeated the stuff I had already heard in church. I still did not have any answers that convinced me that I would be “saved” if I “believed in Jesus,' and that I could know, without a doubt, that Jesus would hear me & save me. I thought that there was absolutely NO way I could ever know for sure that I believed in Jesus & was saved. By this time my life was consumed with fear; fear that I had missed something; fear that there was a missing link somewhere that I would never find. Fear that was I facing a tragic future.
I was miserable, hopeless, and helpless. I realized that all the things “I” was doing were not getting me any answers. I did not know what I should do. One night as I lay down to try and get some sleep, I looked up at the ceiling of the bedroom and said a prayer to a God who I wasn't sure existed. I said “God will you show me how to believe in Jesus?” Then I went to sleep and slept better that night than I had slept in a long time.
The next night I found the big family bible, dusted it off, and turned to the Book of John, the Gospel of John. That was the first time I had ever read in a bible outside of church. I did remember someone in church saying that if anyone wants to know about Jesus to read the Book of John.
As I began to read from the first verse of the Book of John I noticed that, for some reason, I was understanding the words I was reading in a way that I had not understood them in the past when reading the bible in Sunday school class as a kid. It was as though there was something inside of me that was enabling me to understand the words. At first it was kind of like a dim light that allowed me to grasp little bits of information that got my attention. When I read the first 14 verses, something inside of me said, “That is Jesus, and he is God who became a man; he created the world everything in it.”
As I continued to read, the light became brighter and I began to see the words I was reading in a different way. When I read John 3:16 it reminded me of all the things I had heard in church about Jesus dying on the cross.
Two verses that really got my attention were John 4:23-24 which said that we worship God in Spirit and in truth, and I saw that I had just found that missing link. That missing link was/is the Spirit of God, the Holy Spirit, and that light just became much brighter as I realized that I was reading my answer from God. Suddenly I knew that God is real and that He was showing me the truth that I had been searching for.
I continued to read, and found 2 other verses that got my attention, John 5:39-40, where Jesus told the Pharisees that they were searching scripture looking for eternal life and those very scripture told of him, Jesus, but they would not come to him so that he could give them eternal life. Then the light became even brighter as I saw that Jesus wanted me to come to Him so He could give me eternal life.
Next, I discovered even more convincing words in John chapter 6, verses 28- 44, where Jesus told those who were questioning him about the work God the Father required of them, and he told them that the work God required of them was to “believe in” the one whom he has sent. IOW, to believe in Jesus. WOW, that really got my attention, and I was still unsure about the word “believe," but I kept reading because, although I wasn't sure what I was going to find, I was willing to accept whatever it would be if it convinced me how to believe in Jesus. In the rest of verses 30-44 Jesus told those who were questioning him that they can't come to him unless God the Father teaches & draws them to him, Jesus, as they hear and learn from him, God the Father. But the verse that turned that light on to full beam for me was verse 37 where Jesus said, “All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out.”
At the moment that God's Spirit turned that light on for me, I “got it.” All the things that I had heard in church as a kid, but did not understand, suddenly made sense to me. I saw that it's all about him. God's Spirit had just convinced me that the finished work of Jesus on the cross paid the penalty for my sin, in full, and that there is nothing that I could do or had to do to make myself acceptable to God for him to save me. I knew that Jesus took care of my sin problem for me, and immediately an enormous sense of relief overwhelmed my troubled soul. The Holy Spirit had just showed me that “believe in” meant to “depend on,” like a child depends on their parents to take care of them. I was convinced that God is real, the the bible is the truth, and that Jesus was waiting for me to come to him so he could save me and change me. I didn't have to try to believe; I couldn't help myself but to do anything except to believe. I could not have stopped myself from believing if I had wanted to. It was as though Jesus was right there in the room with me; no, I did not see a vision of Jesus, but I knew he was alive and there with me. I found myself talking to him, thanking him for dying on the cross for me, and I asked him to forgive my sin and to change me. I asked him to change me “his way.” I didn't really know what that meant, but that's what I wanted. Actually I came to “believe in” or to “depend on” Jesus before I called on Him. Like Romans 10:13-14 says, “...how shall they call on Him in whom they have not believed?”
That night, over 50 years ago I found a peace that I still have today. It is a peace that is impossible to explain to anyone who has never found that peace for themselves.
Yes, sometimes the devil tries to discourage me by putting the doubts back in my mind. He will try to get me to question my faith by telling me “you didn't really have enough faith,” or “ you didn't really commit your life to Christ,” or you didn't really repent,” or you didn't confess all your sin.” I remind the devil that it is not about anything I did, but it is all about what Jesus did for me on the cross. I will quote verse 3 of my favorite hymn to him.
My sin oh the bliss of this glorious thought
My sin not in part, but the whole
Is nailed to the cross and I bear it no more
Praise the Lord, Praise the Lord Oh my soul
It Is Well with My Soul, Horatio G. Spafford
And then I quote my favorite scripture to him: John 14:6, “Jesus said I am the way, the truth, and the life: no man cometh unto the Father, but by me.”(KJV)
John
