The mere asking of the question, “Will I go to heaven?” indicates that a person believes heaven exists — a good starting point. In any religion except Christianity, the answer is always: “You can’t know for certain because you never know when you’ve done enough good to overcome the bad.”
That also carries for some Christian groups, such as many pre-Vatican II Catholics, who arrive at the same point in various ways.
For Christians of conservative Lutheran and those with Reformed origins, two responses dominate. The Reformed tend to rely on Romans 10:9 (ESV), “if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved.” Lutherans rely first on, “For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast.” (Ephesians 2:8-9, ESV).
Whether a person is “believing in one’s heart” or seeing that it is “by grace you have been saved through faith,” both point to faith as the key factor. It’s just that the first is not nearly so comforting as the second. The faith expressed in Romans 10 is entirely subjective to the person. Is there a feeling in the heart that strongly, completely believes in the risen Jesus? On most days, faithful Christians will testify to this feeling. But other times, they doubt themselves, questioning if they really believe because they lack a certain warm, fuzzy feeling that Jesus is in their heart – the subjective. Such feelings can wane much as love and affection in certain marriages.
The Lutheran foundation, on the other hand, points to God doing the saving, not the person’s determining level of faith. If God has saved the person purely by grace, then even the smallest tidbit of faith that Jesus rose from the dead is enough. Jesus once compared powerful faith to something the size of a mustard seed, which has power to move mountains. So faith is a gift of God and he promises not to take back such a gift. We say this method is objective because it depends on God’s work, not the person’s feelings.
So do you want to know if you’re going to heaven, Christian? Then read Ephesians chapter 2 and wander through Romans chapter 3. Cling to the objective truth that salvation (going to heaven) is by grace alone, faith alone, and God’s Word alone.