The illustration shows two lines coming to a point. This suggests narrowing down. It is the opposite of the "Expand" picture, which showed something getting wider and opening up. The arrow shows that the movement is toward this "contracting" or narrowing down. Contract is the opposite of expand.
After having found the thinking target the next stage is to expand upon it and say as much about it as possible. The final stage is to contract down to what is important.
* Pick out the main points