I think you cannot be sure of anything beyond the truth of God's love. That's part of the challenge of living, that we cannot be sure. Believing in the Bible is a way for people to feel sure, but it's all based simply on a belief, nothing more.
I think that we can live with faith without hanging our faith on rigid adherence to a particular doctrine. I think that Christianity is one path to knowing God. It's one path among many. Christianity is no more true than any other faith is, in my view. It's no less true either. I think that people can grow closer to God through Buddhism and through Judaism and through paganism, just as we can grow closer to God through Christianity.
For me personally, the practice of faith does not require adherence to a particular doctrine. I am fine with not knowing. I believe that as humans, we can know only a portion of truth, never the whole of it.
Today is my birthday. It's my first birthday since my father passed away this past May. His passing was gentle, and God spared him and us anguish in that. I had the blessing of being with my dad for the last 10 hours of his life, as he died. It was a profoundly moving experience and a great blessing. We talked about our love for each other, and he said, "You've made me very happy. I want you to know that." Of course, I knew that, and it was great to share it with him again.
My dad has always accepted me as a gay person. That was never a barrier between us. We have always been very close. I feel sad in the small moments, like when the Red Sox won the World Series this year, and he wasn't here to see it. Or on my birthday, and he isn't here to share it with us. He told me, though, as he lay dying that he was comforted that I have my daughter. And I love my daughter the way he loved me, and that's a deep love, a love that flows from God. I have much to be thankful for on this day.