God created us to be fruitful, but He did not want our fruit to be a result of our effort. Fruits on a fruit tree is a result of the life inside of the tree. In the same way God placed His Spirit inside of us, because He wanted the fruits in our life to be a result of His life inside of us. In other words, we are not suppose to manufacture the spiritual fruits in our life — they will automatically come, if we make sure to stay connected.