The Holy Spirit (Hebrew: רוּחַ הַקֹּדֶשׁ, Modern ruach hakodesh, Tiberian ruaħ haqqodɛʃ) in Judaism, also termed "Divine Inspiration," generally refers to the inspiration through which attuned individuals perceive and channel the Divine through action, writing or speech. Through this they attain some degree of prophetic knowledge, and possibly convey it to others.
The phrase ruach hakodesh (also transliterated ruaḥ ha-qodesh) is used in the Tanakh and other writings to refer either to the spirit of inspiration as above, or to the general, indwelling revelation of the Divine Presence among the Jews, also known as the Shekhinah. Although the term appears frequently in post-biblical writings, in Scripture itself, the term appears only in possessive form as רוּחַ קָדְשְׁךָ ruach kadshkha "Thy holy spirit" (Psalms 51:11), and as רוּחַ קָדְשׁוֹ ruach kadsho, "His holy spirit" (Isaiah 63:10,11). Later writings identify other scriptural instances of the word רוּחַ ruach, "spirit," as indicating ruach hakodesh.
"Holy Spirit" can indicate the general ability to perceive Divine revelations shared by all prophets. For example, Rabbi Moshe Chaim Luzzatto writes about the general return of prophecy in the Messianic Era using this term. In the Kuzari, Judah Halevi corroborates that "Holy Spirit" indicates prophecy of various levels, and adds further that righteous leaders of the Jewish people such as kings and the High Priest of Israel are also granted the Holy Spirit to guide them.
Holy Spirit can also be used more technically to indicate a specific level of inspiration. Among the various levels of prophecy, Holy Spirit is one of the lowest levels, and is strictly speaking not considered prophecy proper. The difference lies in the intensity of the experience, and the lack of knowledge that the revelation is an actual prophecy. According to Maimonides, a person experiencing this revelation would feel the spirit enter him and give him the power and motivation to speak. The subject could be of science, a psalm, a moral message for those around him, or an exposition of political or theological knowledge. This would occur while he was conscious and in the full possession of his senses, though the revelation could also come in a dream. Several books in Scripture such as the Psalms, Book of Daniel, and Book of Esther were written with this Holy Spirit, and their authors are thus only called prophets in the more general sense of the term.
The above is different from true prophecy in a few ways. A proper prophet would have no doubt about his status as a prophet; he would know definitely without any uncertainty that his revelation was a true prophecy. Also, while one with Holy Spirit would retain control over his body and senses, a prophet's limbs would tremble, his physical powers would weaken, and he would lose control of his senses in order that his mind be able to focus entirely on the revelation. (The sole exception to this is Moses, who retained his composure during prophecy.)
In general, the prerequisites for the Holy Spirit are similar to those for actual prophecy. For example, the Holy Spirit would only rest upon one who was happy. It was therefore common in the Temple Era for the Holy Spirit to rest on Jews participating in the festivities of song and dance during Simchat Beit HaShoeivah, and musicians would often accompany prophets at other times of the year. With the death of the later prophets Haggai, Zechariah and Malachi and the concurrent persecutions of the Jewish people, achieving a state of happiness was difficult, and so prophecy and the Holy Spirit ceased among the Jews. However, the echo of the heavenly voice known as the bat kol continued, since this is a lesser level of revelation than the Holy Spirit.
The Jerusalem Talmud lists a series of other requirements, such as cleanliness, humility and fear of sin. Eating only kosher food is also mentioned in Akeidat Yitzchak 60:15, and the benefits of this for general spiritual sensitivity are echoed elsewhere in the Talmud and in Chassidic literature.
Sin could also drive away the Holy Spirit. Commenting on David's request for forgiveness in Psalms 51:13, Abraham ibn Ezra writes that David was afraid of falling from the level of men of the Holy Spirit.
The term is discussed in the Babylonian Talmud, Makkot 23b and elsewhere. Rabbinical use is discussed by Joseph Jacobs and Lajos Blau in the article "Holy Spirit" in the Jewish Encyclopedia of 1911.
In Judaism, God is One; the idea of God as a duality or trinity is considered shituf (or "not purely monotheistic"). The term ruacḥ haQodesh is found frequently in Talmudic and Midrashic literature. In some cases it signifies prophetic inspiration, while in others it is used as a hypostatization or a metonym for God. The rabbinical understanding of the Holy Spirit has a certain degree of personification, but it remains, "a quality belonging to God, one of his attributes".
In Rabbinic Judaism references to the spirit of God abound, however apart from certain strains of Kabbalistic mysticism it has rejected any idea of God as being either dualistic, tri-personal, or ontologically complex.