ANSWER: He probably told you that there is a great difference between unbelief and doubt. Unbelief, involving as it does a permanent wrong attitude of the will inconsistent with spiritual life, is always sinful; and doubt, not implying any fixed and wilful repugnance to saving truth, but rather a temporary suspense of the mind while investigating a theological proposition with a willingness to receive the truth, is not a sin. A man may doubt and yet live on the right side of his doubts. Bunyan tells us that Christian fell into the slough of despond and got out on the right side of his doubts, the side towards the celestial city; and that for a while he was in Doubting Castle, locked up in a cage. Neither of these experiences were destructive of his spiritual life, yet both have their perils. Your preacher should have told you that there is a perfect salvation from doubts on fundamentals. But perhaps he has not got so far in his personal experience as the full assurance of faith, the sure cure of doubt. This is a distinctively Christian privilege unknown to John the Baptist in Herod's dark prison, and to Elijah, his antitype, under the juniper tree. They were the greatest Old Testament saints. The weakest one in the kingdom of heaven opened on the earth on the Day of Pentecost is greater in privilege and experience. He may be entirely delivered from doubt on the fundamentals, and march with firm steps to the fires of martyrdom.
— Steele's Answers pp. 120, 121.