One Block of Genuine Swiss Cheese.
Some form of light source.

Show block of Swiss Cheese make the point that it presents itself as impenetrable.
(Light won't show through it.)

Remove a thin slice. Make the point that when separated from the block of cheese the holes become apparent.

Question: Pretend you are a cheese connoisseur. When you eat a piece of Swiss Cheese do you taste the holes or the cheese?

Now pretend that each piece of swiss cheese represents an individual believers faith.

Illustration Points:
When we are compacted together one members weak areas can be covered by another's strengths.

If the swiss Cheese is any good it will be virtually impossible to cut a slice that doesn't have at least one hole in it.

What does that tell us about bragging about how much faith we have?

I have heard Faith Preachers and Healers make the statement that if there is any doubt in the house God won't move. Hogwash!

Doubt is the absence of Faith; like Cold is the Absence of Heat; like Darkness is the Absence of Light...

Doubt is therefore intangible *if* any Faith is present.

God, like the Cheese Connoisseur, tastes Faith not the lack of it.

Therefore, offer to God the Faith you do have and trust Him for a 'Gift of Faith' if it isn't enough.

Don't frustrate the Grace of God by telling God He can't do something because you don't have mountain moving Faith.

Or, someone has doubts about healing, or, whatever.