A fool according to the Bible is a person who refuses God’s teaching. A fool may be a knowledgeable and intelligent person and yet be a fool according to the Bible.
Since the general nature of a fool is to reject God and his teaching they tend to speak words about things they refuse to understand from God. They are consumed by their own words (12). A fool starts out by talking foolishness and ends up saying crazy things that are dangerous to themselves and others (13).
A fool rejects God’s wisdom as proclaimed in this book. The conclusion of Ecclesiastes is that we fear God and keep his commandments for this is the duty of man. It continues that thought with the truth that we should enjoy the labors of our hard work under the sun; stop, take time to enjoy the gifts of God, and be good to others. A fool rejects this. Instead, they work until they are so weary they cannot even find their way to their home (in those days all lived in villages, towns, and cities.)
A wise person who obeys God speaks gracious words (12). They may not know what is specifically coming (14). However, they know that it is good to trust God and his teachings. When asked why they believe this they tell others that it is good to have faith in God’s good intentions for their life.