Holy Spirit in Christianity

Most Christian denominations believe the Holy Spirit, or Holy Ghost, to be the third divine Person of the Trinity, a triune god manifested as God the Father, God the Son, and God the Holy Spirit, each being God. Nontrinitarian Christians, who reject the doctrine of the Trinity, differ significantly from mainstream Christianity in their beliefs about the Holy Spirit. In Christian theology, pneumatology is the study of the Holy Spirit. Due to Christianity's historical relationship with Judaism, theologians often identify the Holy Spirit with the concept of the Ruach Hakodesh in Jewish scripture, on the theory that Jesus was expanding upon these Jewish concepts. Similar names, and ideas, include the Ruach Elohim (Spirit of God), Ruach YHWH (Spirit of Yahweh), and the Ruach Hakodesh (Holy Spirit). In the New Testament the Holy Spirit is identified with the Spirit of Christ, the Spirit of Truth, and the Paraclete (helper).

The New Testament details a close relationship between the Holy Spirit and Jesus during his earthly life and ministry. The Gospels of Matthew and Luke and the Nicene Creed state that Jesus was "conceived by the Holy Spirit, born of the Virgin Mary". The Holy Spirit descended on Jesus like a dove during his baptism, and in his Farewell Discourse after the Last Supper, Jesus promised to send the Holy Spirit to his disciples after his departure.

The Holy Spirit is referred to as "the Lord, the Giver of Life" in the Nicene Creed, which summarises several key beliefs held by many Christian denominations. The participation of the Holy Spirit in the tripartite nature of conversion is apparent in Jesus' final post-resurrection instruction to his disciples at the end of the Gospel of Matthew, "Make disciples of all the nations, baptizing them into the name of the Father and of the Son and of the Holy Spirit." Since the first century, Christians have also called upon God with the trinitarian formula "Father, Son and Holy Spirit" in prayer, absolution and benediction. In the book of the Acts of the Apostles the arrival of the Holy Spirit happens fifty days after the resurrection of the Christ, and is celebrated in Christendom with the feast of Pentecost.

The Koine Greek word pneûma (πνεῦμα, pneuma) is found around 385 times in the New Testament, with some scholars differing by three to nine occurrences. Pneuma appears 105 times in the four canonical gospels, 69 times in the Acts of the Apostles, 161 times in the Pauline epistles, and 50 times elsewhere. These usages vary: in 133 cases it refers to "spirit" and in 153 cases to "spiritual". Around 93 times, the reference is to the Holy Spirit, sometimes under the name pneuma and sometimes explicitly as the pneûma tò Hagion (Πνεῦμα τὸ Ἅγιον). (In a few cases it is also simply used generically to mean wind or life.) It was generally translated into the Vulgate as Spiritus and Spiritus Sanctus.

The English terms "Holy Ghost" and "Holy Spirit" are complete synonyms: one derives from the Old English gast and the other from the Latin loanword spiritus. Like pneuma, they both refer to the breath, to its animating power, and to the soul. The Old English term is shared by all other Germanic languages (compare, e.g., the German Geist) and it is older; the King James Bible typically uses "Holy Ghost". Beginning in the 20th century, translations overwhelmingly prefer "Holy Spirit", partly because the general English term "ghost" has increasingly come to refer only to the spirit of a dead person.

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What the Hebrew Bible calls "Spirit of God" and "Spirit of Elohim" is called in the Talmud and Midrash "Holy Spirit" (ruacḥ ha-kodesh). Although the expression "Holy Spirit" occurs in Ps. 51:11 and in Isa. 63:10–11, it had not yet acquired quite the same meaning which was attached to it in rabbinical literature: in the latter it is equivalent to the expression "Spirit of the Lord". In Gen.1:2 God's spirit hovered over the form of lifeless matter, thereby making the Creation possible. Although the ruach ha-kodesh may be named instead of God, it was conceived of as being something distinct; and, like everything earthly that comes from heaven, the ruach ha-kodesh is composed of light and fire. The most characteristic sign of the presence of the ruach ha-kodesh is the gift of prophecy. The use of the word "ruach" (Hebrew: "breath", or "wind") in the phrase ruach ha-kodesh seems to suggest that Judaic authorities believed the Holy Spirit was a kind of communication medium like the wind. The spirit talks sometimes with a masculine and sometimes with a feminine voice; the word ruacḥ is both masculine and feminine.