Doubt is the earliest stage in the sin of unbelief. When God says something and a person doubts it, soon, it would result in disbelief by the same person. Doubt was the first seed that the serpent sowed in the mind of Eve.
God told Adam initially that anyone who would eat of the fruit of the tree of knowledge of good and evil would die. Yet, when Eve was talking with the serpent, it led the woman to doubt God’s word. Soon, doubt resulted in sin, not only of Eve but Adam as well.
Seeds of doubt should be plucked out from the ground of the heart as early as possible. If left unchecked, this doubt may grow into the sin of disbelief, which causes even the most faithful Christians to turn away from God.