When someone sees a friend in trouble, often their first instinct is to throw more wood on the fire. Offer more advice. Lend them a book. Give them more instructions. More often than not, this action has the effect of putting out the fire.
Spark represents the person's desire to change.
The more spark, the stronger the desire to achieve the result. I often ask people to quantify their spark, to assign a number to the intensity of their desire for the result. Nobody likes to do this. We rate the spark on a scale from zero to ten. Zero means no desire.