C. We Believe in the Holy Spirit

And in the Holy Spirit, the Lord, the giver of life,who proceeds from the Father. 

With the Father and the Son he is worshipped and glorified. 

He has spoken through the Prophets.

(Symbol of Faith)

Through him the Holy Spirit was made manifest, 

the Spirit of truth,the grace of sonship, 

the pledge of the inheritance to come, 

the first fruit of the eternal good things,

the life-giving power, the source of sanctification.

(Anaphora of the Liturgy of Saint Basil the Great)

91. The  Holy  Spirit  is  the  Third  Divine  Person  and  proceeds  from  the  Father(see Jn 15:26). This procession [i.e., coming forth] of the Holy Spirit  can  be  explained  through  an  image,  making  use  of  an  analogy:  the Father is the source, the Son is the stream, the Holy Spirit is the water. There is only one source for the stream and the water, only one Father for the Son and for the Holy Spirit, which like water flows from the  source  and  fills  the  river-bed  and  stream(See Tertullian, Against Praxeas, 8). The  Holy  Spirit  is  a  Divine Person that is equally worshipped and glorified with the Father and the Son, proceeding from the Father, coming to rest in the Word, and expressing the Word.(See John of Damascus, Exact Exposition of the Orthodox Faith, I, 7)
92. The Holy Spirit is often compared to breath, by which the spoken word resounds.  Appropriately,  within  the  Most  Holy  Trinity,  the  Father  speaks  the  Word (begets  the  Son)  by  the  Holy  Spirit:  “And  it  is  this  [Breath]  which  in  the  moment  of  utterance  becomes  the  articulate  word, revealing in itself the force of the word.”(John of Damascus, Exact Exposition of the Orthodox Faith, I, 7) 

1. The Holy Spirit Revealed in the Holy Scriptures

93. In Holy Scripture, the word spirit (in Hebrew, ruah) shares a common root with the verb to breathe. It means breath, wind, and air. Human life is dependent upon breathing, and when breathing ceases, life ends. We are not masters of our own lives—God gives us life by the life-giving Spirit.
94. From the first sentences of the Book of Genesis, “the Spirit of God”is the image used to signify the living God (Gn 1:2). In the account of the creation of humankind, the Holy Scriptures mention “the breath of life,” which God “breathed into” the man, who then became a “living being” (see Gn 2:7). In the Old Testament, many other images are brought forth as examples that in the New Testament become symbols of the Holy Spirit: “rivers of living water” (Jn 7:38), “anointing” (1 Jn2:20, 27), “fire  of  purification” and “tongues  as  of  fire” (Lk  3:16;  Acts2:3), “wind” (Jn 3:8; Acts 2:2), “seal of anointing on us”(2 Cor 1:22; Eph1:13; Eph 4:30), the laying on of hands(see Acts 6:6; Acts 8:17-19), and “dove ” (Mt 3:16).
95. The New Testament gives the Holy Spirit various titles that emphasize his personhood and divinity: “Advocate” (Jn 14:16); “Spirit of truth” (Jn16:13),  “Spirit  of  adoption” (Rom  8:15),  “Spirit  of  Jesus  Christ” (Phil1:19), “Spirit of the Lord” (2 Cor 3:17), “Spirit of God”(Rom 15:19), and  “Spirit  of  glory” (1  Pt  4:14).  These  titles  indicate  that  the  Holy  Spirit  is  the  Lord  of  life,  and  for  this  reason  we  refer  to  him  as  “the  Lord, the Giver of life.” The Anaphora of Saint Basil the Great refers to  the  Holy  Spirit  as  the  “life-giving  power,”  which  is  the  “source  of  sanctification,” and the “first fruit of the eternal good things.”
96. Christ points to the unique mission of the Holy Spirit in the history of salvation: “When the Advocate comes, whom I will send to you from the Father, the Spirit of truth who comes from the Father, he will testify on my behalf ” (Jn 15:26-27). As Christ had prophesied, the Holy Spirit “will teach you everything, and remind you of all” (Jn 14:26), “he will guide you into all the truth; ... he will declare to you the things that are to come” (Jn 16:13). “He will glorify me [i.e., the Son], for he will take what is mine and declare it to you [the disciples]”(Jn 16:14).