Do you believe that you can’t come to Christ because he would never accept and forgive you even if you did?
There is a sin that would produce this result - a sin that God won’t forgive. Because such a sin is possible, you need to know what it is so that you can know how to avoid it.
We see that those who are concerned about having committed this sin have not actually done so as yet. We also see that only by coming to Christ for salvation can we be fully and finally safe from any possibility that we might commit the unpardonable sin.