"Abracadabra" is a magical chant often used by magicians these days to perform tricks. The spell "abracadabra" was used earlier to calm the bad spirits and cure diseases. It was believed that when the spell was worn as an amulet around the neck or around the arm, the bad spirits would disappear.
The spell can't be chanted and it is usually written in a triangular shape with a single letter missing in each row as we go down the triangle, and at the end only the letter "a" remains. Then an amulet in the shape of locket or armlet is made using this paper. The belief is that as each letter disappears from the spell, so does the disease and in the end only "a" remains, proving complete recovery of that person.
It is said that the spell should be written and not chanted. Chanting does not hold any magical power. But there are other people who believe that chanting the spell "abracadabra" invokes the paranormal spirits and uses their magical powers to cure illness.
The folklores suggest that the chant is related to the word "abraxas" used as amulets worn by people of the Late Roman Empire. The amulet was supposed to cure people who were suffering from illusions by arousing the paranormal spirits. There are many places where amulets of this spell are worn around the neck and arm. Though it is not a very widely used good luck charm and people don't have too much faith in it, there are others who swear by it.
Chanting verses and casting spells have always been a part of cultures around the globe. It is an individual choice of believing or defying them. But historical facts do talk about some extra terrestrial forces, which goes on to prove the existence and effectiveness of these verses and spells. This makes us think at least once that there might be something to it, though scientifically nothing proves this phenomenon.