Let me share a testimony...
About 5 or 6 years ago my brother-in-law's dad got saved and (I'll call him Mark - not his actual name) Mark began to show an interest in spiritual issues. One day about 5 years ago, after talking to my sister, I shared the gospel with him - drew it out. After a short discussion, I remember asking him if he'd like to see an illustration about what it meant to be a Christian. he said, "love to!"
So I laid out the gospel message, looking up a few appropriate verses, and then I suggested a "prayer," then asked him if that expressed a desire on his own heart. Tears ran down his cheeks as he said "yes." So we prayed together. I made it clear to him that the actual words of the prayer were not what saved, but that his faith in Christ, trusting in His death in his palce, was what God saw. There was no doubt about his sincerity, and his joy afterwards was so exciting.
His life changed significantly after this. he began going to church every week, and spent time in the Bible regularly. But after about two years he became frustrated about something involving the church. I tried to work through it with him, and eventually suggested that he attend a different church, suggesting some in their local. Eventually though, he stopped attending. he was still very positive about the Lord, but felt that he didn't need to go to church. After a year and a half or so, he became more and more bitter, and some serious lifestyle issues became apparent. He no longer goes to church, and has no interest in God. My sister last told me that he told her that he no longer believes in God.
But I realize that he may return to the Lord. However, what if he never does? One thing I am confident about: he genuinely trusted in Christ about 5 years ago.
Now I realize that we should not use testimonies to determine theology, but some testimonies have already been shared and hypothetical ones suggested. This one is real. I have absolutely no doubt that I will see him in the kingdom.
FA