The Erinyes were three goddesses of revenge and justice. They lived in the depths of the earth and had a very important mission: to make sure that those who did bad deeds would face the consequences of their actions.
The first of the Erinyes was Alecto. Alecto was the goddess of endless rage. When someone did something very bad, like hurting others or being very unfair, Alecto was there to remind everyone that wrath can come when we don't behave properly.
The second was Tishiphone, the Erinyes of the punishment of the murders. Tishiphone had the duty of ensuring that those who committed the serious crime of murder would face justice. People feared her but also respected her for her dedication to justice.
The third was Megaira, the goddess of jealousy and revenge for family offences. Megaira saw to it that those who betrayed their family or harmed their own people were punished.
Despite their serious mission, the Erinyes were not bad. They were there to keep the balance and make sure that justice was done. People respected them because they knew that the Furies protected what was right and just. When someone sincerely repented for their wrongs, the Furies could show mercy and forgive them.