And Zacharias said unto the angel, Whereby shall I know this? for I am an old man, and my wife well stricken in years.
Then said Mary unto the angel, How shall this be, seeing I know not a man?
Zacharias and Mary were both visited by an angel. Zacharias and Mary were both told to fear not. Zacharias and Mary were both told they would have a child. Zacharias thought he was too old. Mary didn’t have a husband. But when told of the LORD’s plan, they had different responses.
Zacharias had prayed for a son (Luke 1:13), but now didn’t believe when the angel told him (Luke 1:18).
Mary hadn’t prayed for a son at this time, but didn’t understand how it could happen (Luke 1:34).
The LORD is ok with you not understanding, but is not ok with your not believing.