What the Bhagavad Gita says about doubt
The Gita is a conversation, not a sermon, and it survives on Arjuna's willingness to interrupt. He asks what the difference is between two words Krishna has been using loosely. He asks what happens to someone who tries and fails. He asks the awkward question about people who worship sincerely without knowing the rules.
That is worth noticing because scriptures do not usually model doubt approvingly. 4.40 is blunt about the cost of unresolved doubt, saying the doubting person has no happiness here or anywhere. But 4.42 tells Arjuna to cut doubt with knowledge and stand up, which treats it as something to work through rather than suppress.
18.10 gives the most interesting phrase on the subject. The settled person is described as one whose doubts are cut, not answered. Some questions never end by acquiring more information, because they were never short of information. They end when whatever was holding them taut is let go.
The verses 11
2.6
And we do not even know which would be better - that we win, or that they win.
2.7
My nature is crippled by a failing that shames me, and I cannot see straight about what is right.
3.2
Your words seem to contradict each other, and they are confusing me.
4.40
The one who does not know, who does not trust, whose self is made of doubt - he is lost.
4.41
Actions do not bind the one who has given his actions over through the practice, whose doubts knowing has cut away, who is in possession of himself.
4.42
So cut this doubt of yours - the one sitting in your heart, born of not knowing - with the sword of knowing.
6.37
Arjuna said: One who has trust but does not strive, whose mind wanders from the practice - failing to reach completion in it, what road does he go, Krishna?
6.38
Fallen from both, without any standing place, confused on the road to the infinite - does he not perish, Krishna, like a torn-off cloud?
6.39
You should cut this doubt of mine completely, Krishna.
18.10
He does not hate the work that is unpleasant and he does not cling to the work that is pleasant.
18.73
Arjuna said: the confusion is gone.