The Holy Spirit
The difference between Christianity and all other religions is Christianity has the Holy Spirit. Without the Holy Spirit Christianity would be just another man made religion.
What is the Holy Spirit? What is the purpose of the Holy Spirit? How do you know if you have the Holy Spirit? Is the Holy Spirit really necessary for today? These are some of the questions I will be addressing in this Bible study using the New King James Version as our guide.
The first question is what is the Holy Spirit? Simply put, the Holy Spirit is the spirit of Jesus Christ living inside of you. In 1 Corinthians 6:19 we read, “Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own?” 
We also see in Romans 8:9 that the Holy Spirit is referred to as “the Spirit of Christ”. “But you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you. Now if anyone does not have the Spirit of Christ, he is not His.
In Colossians 1:27 we read. “To them God willed to make known what are the riches of the glory of this mystery among the Gentiles: which is Christ in you, the hope of glory.” 
We also see that the Holy Spirit is actually the Spirit of Jesus Christ as stated in Galatians 4:19, “My little children, for whom I labor in birth again until Christ is formed in you,” 
As we can see the Holy Spirit has several different names, some of the names we have encountered in the Bible are, The Spirit, Christ in you, the Spirit of God, the Helper, the comforter, the Spirit of Truth and the Spirit of Christ.
The Holy Spirit is the power of God living inside of you. In Romans 15:13 we read, “Now may the God of hope fill you with all joy and peace in believing, that you may abound in hope by the power of the Holy Spirit.”
This shows us Christians just how dependent we are on the Spirit of God for our very survival. Even new Christians to the faith have to understand that it’s not their power that keeps them as Christians but it’s the power of God’s Holy Spirit. 
We can see that in John 15:5, “I am the vine, you are the branches. He who abides in Me, and I in him, bears much fruit; for without Me you can do nothing.
Without Christ we can do nothing but with Christ we can do all things! That verse is found in Philippians 4:13, “I can do all things through Christ who strengthens me. 
We can now see that one of the purposes of the Spirit of Christ is to empower us to do the will of God. I know some people are thinking I am afraid God will ask me to do something I don’t want to do. According to God’s word God’s Spirit who is inside of you has that taken care of that problem. In Philippians 2:13 we read, “For it is God who works in you both to will and to do for His good pleasure.”
Once you trust God you will discover that there is no greater joy on this planet than when you find yourself doing God’s will and it turns out that it was also your will.
Another very important function of God’s Holy Spirit is to communicate with you that you belong to God and you are “a child of God”. The Bible says in Romans 8:16-17, 
“The Spirit Himself bears witness with our spirit that we are children of God, and if children, then heirs-heirs of God and joint heirs with Christ, if indeed we suffer with Him, that we may also be glorified together.”
By reading this verse you can see that by accepting Jesus and asking for Christ’s Holy Spirit at some point in time the Spirit will bear witness with our spirit that we are a “child of God”. There can be no doubt for the true Christian believer that we are a child of God and that our heavenly citizenship is assured. I have heard it said by many people that we can't know if we are going to heaven until we die. According to this last verse that statement is false.
The Bible says in James 4:8 “Draw near to me and I will draw near to you.”
The closer we move towards God the more we will experience Christ’s Holy Spirit in our lives. We move closer to God by the daily reading of His word and by daily prayer.
The Bible says God gave us His Spirit as a “guarantee” of our citizenship in heaven and He has sealed us until the “day of redemption.” In 2 Corinthians 5:5 we read, “Now He who has prepared us for this very thing is God, who also has given us the Spirit as a guarantee.” 
In 2 Corinthians 1:22 we read “who also has sealed us and given us the Spirit in our hearts as a guarantee.” And in Ephesians 4:30, we read “And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption.”
If then God has “sealed” you and guarantees your place in His kingdom then the only one who can remove this seal on you is God and God says in Hebrews 13:5, “I will never leave you nor forsake you.”
By reading these scriptures it shows us that once we are saved we are secure in God’s kingdom.
How do we receive the Holy Spirit? In Ephesians 1:13 we read. “In Him you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also, having believed, you were sealed with the Holy Spirit of promise,”
So if we take this verse apart we can then see just how we are to receive the Holy Spirit. This verse says “In Him (Jesus) you also trusted, after you heard the word of truth, the gospel of your salvation: (The gospels in the Bible are the books of Matthew, Mark, Luke and John.)  
After reading these books we need to ask ourselves, Do we believe these books and do we trust Jesus? If the answer is yes then according to God’s word you will be sealed with God’s Holy Spirit. The next two verses will verify that the gospels (the good news of Christ’s sacrifice) contain the power of God to give you the power to live the Christian life.
1 Thessalonians 1:5, For our gospel did not come to you in word only, but also in power, and in the Holy Spirit and in much assurance, as you know what kind of men we were among you for your sake.
Romans 1:16
 For I am not ashamed of the gospel of Christ, for it is the power of God to salvation for everyone who believes, for the Jew first and also for the Greek.
The Bible also says in Luke 11:13 “If you then, being evil, know how to give good gifts to your children, how much more will your heavenly Father give the Holy Spirit to those who ask Him.”
After reading the gospels don’t forget to ask God to fill you with the Spirit of Jesus Christ.
What is the purpose of the Holy Spirit? The Holy Spirit has many functions. The Holy Spirit called the “Helper” as written in John 14:16, “And I will pray the Father, and He will give you another Helper, that He may abide with you forever- I have heard sermons where the Pastor said that the Holy Spirit is for today only and after we die He is no longer needed. According to this last verse the Holy Spirit will live in us forever.
In John 14:26 we read, ”But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all things that I said to you.”
In John 15:26 we read, “But when the Helper comes, whom I shall send to you from the Father, the Spirit of truth who proceeds from the Father, He will testify of Me.”
The Holy Spirit also known as the Helper and the Spirit of Truth is here to testify to our spirit of the truth and majesty of Jesus Christ. I believe the Holy Spirit is here to confirm our citizenship to the kingdom of heaven. I also believe the Holy Spirit is here to make us one with the Father and the Son as the next prayer of Jesus would indicate in John 17:20-23;
Jesus Prays for All Believers 
“I do not pray for these alone, but also for those who will[a] believe in Me through their word;  that they all may be one, as You, Father, are in Me, and I in You; that they also may be one in Us, that the world may believe that You sent Me.  And the glory which You gave Me I have given them, that they may be one just as We are one:  I in them, and You in Me; that they may be made perfect in one, and that the world may know that You have sent Me, and have loved them as You have loved Me. That they also may be one in Us.

Who is Us? That would be the Father, the Son, and the Holy Spirit. Do you remember the end of the verse in John 14:16, “And I will pray the Father, and He will give you another Helper, that He may abide with you forever- We will be one with the Father, Son, and Holy Spirit. What an honor!  We all need to meditate on this for a while, not just for what this means to our future but also what this means to the present.
How do you know if you have the Holy Spirit living inside of you? To answer this question we need to see what the characteristics of the Holy Spirit are. 
We can see these characteristics in Galatians 5:22-23, “But the fruit of the Spirit is love, joy, peace, long suffering, kindness, goodness, faithfulness, gentleness, self control. Against such there is no law.”
We also see in 2 Corinthians 5:17 that there is definitely a change of character in the new believer.  
Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new. 
The Bible also says that we as Christians should also test ourselves as stated in 2 Corinthians 13:5 “Examine yourselves as to whether you are in the faith. Test yourselves. Do you not know yourselves, that Jesus Christ is in you?—unless indeed you are disqualified.” 
How do you test yourselves? Once you become a Christian you will see things differently than you did before and gradually you will start to see a change in yourself with the characteristics as stated above in Galatians 5:22-23.
Is the Holy Spirit for today? Yes!! Without the Holy Spirit you don’t have a guarantee that you are a child of God.  You don’t have God’s power to get you through all the hardships of this life nor do you have His companionship all of which we desperately need.
In 1 John 4:4 we read, “You are of God, little children, and have overcome them, because He who is in you is greater than he who is in the world.
One of the purposes of the Holy Spirit is for us to become one with Christ. Without the Holy Spirit residing in us that would be impossible leading to drastic results as we can see in the next few passages. 
In Romans 8:9 we read, “But you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you. Now if anyone does not have the Spirit of Christ, he is not His. 
In Matthew 7:23 Jesus says, “And then I will declare to them, ‘I never knew you; depart from Me, you who practice lawlessness!” 
Is the Holy Spirit necessary for today? Not only is the Holy Spirit necessary for living the Christian life today the Holy Spirit is essential for going to heaven. Without the Holy Spirit living inside of you, all you have is a useless man made religion. Your heavenly existence is highly questionable and very doubtful as we see in these next passages. 
In 1 Corinthians 6:14 we read, “And God both raised up the Lord and will also raise us up by His power. 
And in Romans 8:11 we read, “But if the Spirit of Him who raised Jesus from the dead dwells in you, He who raised Christ from the dead will also give life to your mortal bodies through His Spirit who dwells in you.  
If you have the Spirit of Christ living inside of you, you will want to keep the commandments of Jesus which are Love God with all your heart and the second one is to love your fellow man as you love yourself. Love is the key. If you find yourself critical with people and have no love in your heart then you need to re-examine yourself and ask God for help.
If after reading this study of the Holy Spirit you find that you don’t have the Holy Spirit living inside of you then I would start over and go back to the beginning which begins at reading the gospels of Matthew, Mark, Luke, and John.
As a child I memorized this next verse and always kept it in the back of my mind. The verse is found in the Old Testament in the book of Isaiah 55:11 which reads “So shall My word be that goes forth from My mouth; It shall not return to Me void, But it shall accomplish what I please, And it shall prosper in the thing for which I sent it.” 
Just as Jesus did His miracles with the spoken word, the Bible, the word of God is the power of God to change you from the inside out.
Go back to the beginning and read the gospels of Matthew, Mark, Luke and John. Before you read, pray that God will open your spiritual eyes so that you may see. When you pray, ask God if these are His words and ask Him to prove to you that Jesus is God. Once God has shown to you that these words are the truth and you believe the gospel is God’s word, and then ask Jesus to come into your life and ask Him to fill you with His Holy Spirit.
Until you know beyond a shadow of a doubt that you are a “child of God” and that you are saved and going to heaven I would always keep this verse close by. “
Ephesians 1:13, “In Him you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also, having believed, you were sealed with the Holy Spirit of promise,”
Also make sure that the Bible you are reading is a good translation.  If you attend church services make sure they teach the Bible, believe in the Holy Spirit and believe that Jesus is the Son of God. 
This is just a short study of the importance, necessity and power of the Holy Spirit. There are many more topics and purposes of the Holy Spirit. We only touched on a few.