Sherry from Baltimore wrote:
I've heard that it's forbidden to cross the fingers of the right hand with the fingers of the left hand. This sounds a bit baffling. And I see Orthodox Jews who do this and wonder if they are ignorant of a prohibition or perhaps just not always aware of the state of their fingers. Thank you for this wonderful service.
Crossing the fingers isn't really a prohibition, but it is mentioned in traditional sources as something to avoid. Here is the explanation of one commentary: "The right side represents Divine mercy whereas the left represents Divine strict judgment, and it is inappropriate for a person to do something that signifies a mixing of these distinct attributes of G-d. It is even a dangerous thing to do, and therefore one should be careful to avoid this practice." This is a deep kabbalistic concept that we cannot truly understand.
I asked a renowned Jerusalem rabbi who said that if you aren't generally concerned about intertwining your fingers then there's no need to be concerned about this. Only if one is generally careful not to cross fingers because of it being wrong or even dangerous does one need to be always careful not to do so.
- Shmirat Haguf V'Hanefesh 78:1