What is a Miracle?:
Normally, a miracle is any event which occurs in contradiction to established natural laws in other words, an event which should normally be considered impossible. Sometimes, the term is used in a broader and more general sense to refer to things which are wondrous, beautiful, and life-affirming. Thus, the smile of a newborn baby is sometimes labeled as a miracle. No gods and nothing supernatural are required to explain such miracles because they are natural aspects of our existence.
Old Testament Miracles:
In the Old Testament, miracles are usually associated with Gods interventions to help the Hebrews and demonstrate his power in other words, to demonstrate that he deserves worship and obedience. These miracles are usually worked through the actions of a person. The most obvious example of this is the entire story of the Exodus from Egypt: over and over Gods power is made manifest in miracles designed to prove that God is sovereign.
Miracles and Exorcisms:
A popular form of miracles among Jews and early Christians was the exorcism: driving demons from the body of a possessed person. Judaism, influenced by Greek philosophy, had slowly been making God more and more transcendent, increasing the need for intermediary figures like angles and humans imbued with divine power. Some of these angelic figures were believed to have rebelled against God, becoming demons and possessing humans. Exorcisms drove the demons out, reasserting Gods sovereignty.
Miracles and Jesus:
Consistent with popular beliefs at the time, the most common form of miracle performed by Jesus was the exorcism. A number of times he is also depicted as healing physical ailments such as leprosy, blindness, and lameness. These miracles were designed not just to demonstrate the power of God, but to act as a sign that the Kingdom of God was coming and would overthrow the evil currently controlling the world.