A voluntary act by which someone or something is regarded with bitter aversion. On the first level hatred is directed against either God or some rational being; on the second level it is directed against some quality in another but without hatred of the individual personality.
Personal hatred of God may take the form of disgust, when a person detests God because he punishes sinners. It is a grave sin because it is contrary to the justice of God. Another form is the hatred of enmity, when a person actually wished evil to God. Such hatred is of its nature diabolical, and is the most grievous of all sins, since it approximates the enmity that the devils have against God.
Personal hatred of a human being is the direct opposite of the virtue of love. Where love inspires a person to wish well to another, hatred arouses the desire to do harm or have harm befall the one hated, not as a source of possible good, but precisely as evil. The gravity of such sins of personal hatred depends on how serious the harm wished or intended, and on how deliberately the malicious desires are harbored.
Hatred or a quality in someone may be either sinful or not. If the hatred is directed only toward some evil quality that a person has, but does not touch that person, it is not sinful. It becomes sinful only if the hatred extends to the person who has some admittedly evil trait or sinful habit. Moreover, it becomes specially sinful when the hatred is directed at some virtue that a person possesses, even when the enmity does not extend to the individual personally.