I would say there are two kinds of doubts: dishonest doubts and honest doubts. Dishonest doubts are both proud and cowardly; they show disdain and laziness. A dishonest doubt is to say, ‘What a crazy idea!’ and then just walk away. ‘That’s impossible’ (or its more contemporary version, ‘That’s stupid’) is an assertion, not an argument. It’s a way of getting out of the hard work of thinking. But by contrast, honest doubts are humble, because they lead you to ask questions, not just put up a wall. And when you ask a real question, it makes you somewhat vulnerable. Mary’s question to the angel actually asks for information and leaves her open to the possibility of a good answer that would cause her to shift her views. Honest doubts, then, are open to belief. If you are really asking for information and good arguments, you might get some.
And here’s what I find wonderful. If she had never expressed a doubt, the angel would never have spoken one of the great statements in the Bible: ‘Nothing will be impossible with God’ (Luke 1: 37 ESV). I’m so grateful for her doubt, because that statement has been comforting and guiding me for years. All kinds of people have been helped immensely by those words. And the only reason we get this extra revelation is because Mary doubted. The more you are willing to express doubt honestly and humbly, the more you bring up your honest questions, the further you, and the people around you, are going to get. I have seen plenty of people who refuse to ask questions and refuse to express their doubts. Some refuse out of hard-heartedness, while others refuse because they think somehow it is disrespectful. Please don’t dare not to raise your honest doubts and questions.
– Tim Keller