Why did Garvey make Cole eat all the contents in the brown paper bag?

Garvey was trying to prove a point. He laid out salt, flour, eggs, baking soda, a bottle of water, sugar, butter, and molasses. He had cole taste them. They tasted bad individually yet together the ingredients baked a cake. He tries to make the point that they taste bad on their own but good together. He wants Cole to be a part of something instead of alone.