So for the past several days I’ve been fleshing out the basic research I had done for the topic, and I see this being a three-part series—the topic is simply too large to be properly treated in a single post. So over the next three weeks, we will treat this topic.
I think that to properly understand the Holy Spirit we must begin at the core of the question and build outward. Therefore, my series will be organized in this way:
Part I: WHO is the Holy Spirit and WHY was He sent?
Part II: HOW does He accomplish His purpose?
Part III: WHAT is the appropriate interaction with Him for the believer?
PART I: Who is the Holy Spirit, and why was He sent to us?
As we begin our discussion on the nature of the Holy Spirit, let me open by referring you to the site of my book, www.riseofthetimelords.com, in what is in no way a shameless plug. At the site, I have posted a sample chapter from my upcoming book, in which I describe the members of the Trinity as a sort of “cross-section” of God fitting within our three-dimensional world. Go read it and then return.
Now the primary point is that we worship a single deity, not three gods sort of mashed together: Father, Son, and Spirit are actually a part of the singular Godhead in the same way that the circular cross-section and rectangular cross-sections of our Pringles can were, as well. (If that made no sense to you, then you didn’t read the sample chapter yet! Go do it now—I am going to refer to it several times.)
So we have one God, but as He tries to step down into our world, we can experience only one cross-section of Him at a time—just as if we stepped into a Flatland, the inhabitants would see only a footprint, not a boot. This concept is rather ancient, actually: even the Jews (who certainly would have balked at anyone saying that they worshipped more than one God!) saw the Spirit as an actual living word, but still not separable from God. 
We see this in Scripture too, of course. The Gospels tell us that the Holy Spirit is sent to us from God at the request of Jesus, and that in fact the Spirit cannot come into our hearts while Jesus is still with us.  His life in some way precluded the Spirit’s indwelling, much as placing the “circle” of the Pringles can into Flatland eliminates the possibility of seeing its rectangular cross-section. So then it is not until Jesus goes away that the Spirit can come into our hearts. Luke reinforces this message, pointing out that Jesus is the one who brings us the Spirit, and that the Spirit of God is equivalent with God and sent from God the Father. 
This definition of the Holy Spirit continues throughout the apostolic letters making up the rest of the New Testament. Paul compares the Spirit to God’s soul, the source of His inner thoughts; he later says that the Spirit is the Lord, and names the three Trinity members explicitly.  In Romans Paul likewise identifies the Spirit as God and says that it dwells inside of us. 
So we can be certain then that we know the Holy Spirit is one member of the Trinity, sent to us by God the Father at the request of Jesus the Son, and that He lives within us.
This, however, is only half of understanding who the Spirit is: we must also understand His role or purpose. Why was He here? God the Father is Creator; Jesus is the Redeemer; so who is the Spirit? What is His core role?
At this point, before answering, I want to discuss my methodology a bit. Often in writing on this blog I begin with the “big idea” and delve down into details, pulling in the Scriptures which support the topic. However, in this case we have a number of widely divergent beliefs in Christianity: the Charismatics will say the Spirits purpose is one thing, the Reformed another, the Catholics another. So if we wish to make any sense of it, we cannot approach it “top-down,” or we will bring our biases into the discussion.
Rather, I am going to build bottom-up in this case. I have gone through the New Testament and identified 155 references to the Holy Spirit. Most of these deal with how He accomplishes His goals (which we will discuss in Part II) or what the appropriate response to Him is (which we shall discuss in part III).
Coming top-down is actually a big problem in this case, for one ends up defining the Holy Spirit merely as the sum of His actions. Rather, when we approach from the bottom-up, we find that there are really only a handful of explicit statements in the New Testament where we are told who He is rather than what He does.
In studying these few statements, I think we can define the Holy Spirit’s purpose as to be:
1. Our inspiration
2. Our witness
3. Our conduit
Let us take each individually.
The most obvious role of the Holy Spirit, and the one which any Christian would list, is that of divine Inspirer. It is the Spirit who divinely inspires the word of God (see Eph 6:17-18, many other passages).
This of course seems obvious—the Holy Spirit inspired the Old and New Testaments and, properly interpreted, they are His word given to us. But Paul actually gives us much more detail than this, in his second letter to the Corinthians:
“You show that you are a letter from Christ delivered by us, written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts. Such is the confidence that we have through Christ toward God. Not that we are sufficient in ourselves to claim anything as coming from us, but our sufficiency is from God, who has made us competent to be ministers of a new covenant, not of the letter but of the Spirit. For the letter kills, but the Spirit gives life.” (2Cor 3:3-6)
In this passage, Paul is contrasting the covenant of the letter (the Mosaic Covenant) and the covenant of the Spirit (the New Covenant of Christ). Paul compares the Holy Spirit to the ink of the New Covenant, and says that the location where He writes is not on tablets of stone (as on Mt Sinai) but rather on our hearts. Thus we become a new living Bible, the epistles of God to the world.
This is a really shocking statement, if you think it through. Paul is not merely being poetical here, but rather is revealing a very impressive truth. When God made His new covenant with us, He did so not with a detailed law written down but through the Spirit in our hearts.
No one who reads this blog can have any doubts but that I love the Scripture. I study it obsessively. I consider it inerrant, as I have written before. It is truly and divinely inspired and is the primary way by which I learn from God.
However…it is the word of God, while Jesus is the Word of God. We must be careful not to devalue God such that He is no more than the words on His page. Never forget that the Bible is God’s letter to us, but that He Himself dwells within our hearts and souls. Too many consider the Holy Spirit’s work completely finished when John put down His pen at the end of Revelation: yet such a position seems untenable, for there is nothing within Scripture to indicate that this is true. This is not typically a problem with Catholics and Charismatics and the Orthodox, but I have indeed known Protestants who worship the “Father, Son, and Holy Scriptures” rather than the “Father, Son, and Holy Spirit.”
When we shrink the Spirit down to being only the sum of His inspiration during the apostolic age, we ironically deny the very Scripture itself, which states that our lives are a living epistle from God to the world and that the Holy Spirit is the ink within us writing our letter.
So we see then that the first role of the Holy Spirit is to provide divine inspiration to men, and (as we shall see in Part II) this manifests itself in the inspiration Scripture, but not only in the inspiration of Scripture. He still works within our hearts even today.
If you have read my suzerain covenants series here, then you are aware that every covenant between a suzerain and a vassal has a witness or series of witnesses. I pointed out at the time that the New Covenant has two witnesses: baptism and communion.
What I failed to notice in a few passages, however, was that there is actually a third: the Holy Spirit. Indeed, I now must amend my prior series to note that Scripture indicates that one of the primary reasons for sending the Holy Spirit is to serve as an eternal witness of the relationship offered between God and man:
“This is he who came by water and blood—Jesus Christ; not by the water only but by the water and the blood. And the Spirit is the one who testifies, because the Spirit is the truth. For there are three that testify: the Spirit and the water and the blood; and these three agree.” 
There are three witnesses sent to testify about Jesus Christ and the New Covenant. First is the water of baptism, which testifies that we have been cleansed of our sins; next is the blood of Christ on the cross, which testifies that the debt is repaid and which we remember through communion; and third is the Spirit of God, which is to provide truthful testimony/witness of the New Covenant.
This is echoed in Hebrews on multiple occasions, most explicitly when the author writes:
“And the Holy Spirit also bears witness to us; for after saying, ‘This is the covenant that I will make with them after those days, declares the Lord: I will put my laws on their hearts, and write them on their minds,’ then he adds, ‘I will remember their sins and their lawless deeds no more.’ ” 
This, then, is the second role of the Holy Spirit: to serve as a witness of the covenant between Christ and man.
The final identity given to the Holy Spirit in Scripture is that He serves as the connection between man and God: He is the conduit that God uses to send us saving grace ; it is through Him that we receive access to God the Father ; He serves as the path for our worship and prayers to reach God ; and He is the One God chooses to judge our sin and sanctify us so that we might grow more spiritual as Christians .
As I read these passages, I have always gotten a definitive feeling of a pipe or conduit—like the Holy Spirit is a cord tethering us to the Father, and transferring things back and forth.
Sure enough, early non-Biblical sources (the letters of Ignatius to the Ephesians) actually make a really great analogy which I think is worth discussing. Ignatius (35-117), a student of John the Apostle, repeats his analogy once in each of his letters to the Ephesians:
“The Holy Spirit does not speak his own things, but those of Christ, and that not from himself, but from the Lord…[you are] chosen stones, well fitted for the divine edifice of the Father, and who are raised up on high by the Christ, who was crucified for you, making use of the Holy Spirit as a rope.” 
In his second letter to the Ephesians, Ignatius expands upon his analogy:
• God is an architect who built a lovely building (the Church);
• We are the stones used to make it up;
• Jesus (the Son) is the one using the machine (the Cross) to raise us to our place in the building;
• The Holy Spirit is the rope connecting us to Jesus and putting us into the proper place in God the Father’s design; and
• Our faith is the pulley through which the rope winds in order to connect us to Christ’s power.
PART I CONCLUSION
It is right that we begin our study of the Holy Spirit by understanding who He is and why He is here. Only when we understand His role can we properly understand what He does in the Scripture and, therefore, how we are to respond.
I like Ignatius’ analogy of a medieval building, where Jesus is operating the Cross to raise our stones, which are connected to Him via our faith (the pulley) and the Holy Spirit (the rope). He uses this to build the Church which God the Father designed.
Regardless of whether that analogy works for you, be aware that the Holy Spirit is the third member of the Holy Trinity, dwells inside the spirits of believers, and does so for three primary purposes: (1) to provide divine inspiration; (2) to be a witness of the New Covenant; and (3) to be the conduit through which we communicate to God.
In our next post, we will learn how the Holy Spirit accomplishes these goals.
 Kohler, Jewish Theology, chapter 32
 John 14:16-26, John 15:26, John 16:7-14
 Luke 3:16-22, Acts 5:3-4, Acts 15:8
 1Cor 2:10-14; 2Cor 3:17-18, 13:14
 Rom 8:11
 1Jo 5:6-8
 Heb 10:15-17
 2Cor 3:6
 Eph 2:18
 Phil 3:3
 1 Pet 1:2
 Ignatius to the Ephesians, chapter 9