Ruach--God the Father

The New Testament teaches that just as God the Father sent Jesus his Son into the world to accomplish his purposes, after Jesus left the earth, he sent another "person" to guide and work in the lives of his people. The New Testament calls this person "the Holy Spirit" (see, e. g., John 14:25-26; 15:26; 16:7-14; Acts 2:1-13, 33; 5:32; etc.). "The Holy Spirit" is not an abstract "thing," an "it," but a "person" who thinks and feels and interacts with other persons both divine and human, etc. Like God the Father and God the Son, the Holy Spirit works through spoken and written words of human beings, but his work is far greater and much more diverse than that. For example, he intercedes for God's people when they pray (Rom. 8:26-27), he participates in the mystery of spiritual growth in the human heart (Gal. 5:22-23), and works in the world and in human lives in many other ways.

At the same time, for reasons beyond human explanation, the Old Testament never refers specifically or unequivocally to the Holy Spirit. Let's note here three passages.
1. Genesis 1:2--Older English versions translated the phrase here: "The Spirit of God moved upon the face of the waters." However, with more reflection and indepth study, it is now clear that the NRSV is correct in reading: "a wind from God swept over the face of the waters," which has parallels in Gen. 8:1 and Exod. 14:21. See good commentaries on this point.
2. Psalm 51:11--Again the NRSV is correct in reading:
"Do not cast me away from your presence,
and do not take your holy spirit from me."
The expression "holy spirit" in line b is parallel to "presence" in line a. Just as "the spirit of Jacob" in Gen. 45:27 is not a separate person from Jacob, but Jacob himself, so God's "holy spirit" in Ps. 51:11 is not a separate person from God, but God [the Father] himself. Linguists call this phenomenon "circumlocution," which means the "use of many words to express what might be expressed by few or one" word(s).
3. Isaiah 63:10-11 [referring to the way the Israelites "treated" God after he delivered them from Egyptian bondage]:
"But they rebelled
and grieved his holy spirit;
therefore he became their enemy;
he himself fought against them.
Then they remembered the days of old,
of Moses his servant.
Where is the one who brought them up out of the sea
with the shepherds of his flock?
Where is the one who put within them
his holy spirit?"
As in Psalm 51:11, here again the NRSV is correct in not capitalizing "holy spirit." This text is referring to the mighty acts of God [the Father]. God's "holy spirit" here is not a separate person from God [the Father], but God himself, who, of course, is holy (see Psalm 99; Isaiah 6:3).
Let me reiterate. The New Testament clearly teaches that God the Father and God the Son sent the Holy Spirit [a "person" separate from themselves] to work in the world and in the lives of human beings. However, the Old Testament nowhere refers explicitly to the Holy Spirit "as a person separate from God the Father and God the Son." There are ample passages in the New Testament which teach important truths about the Holy Spirit as a separate person. The use of Old Testament texts to refer to this "person" is misguided.