Is it possible to be a Christian without the Holy Spirit? Silly question, isn't it? Of course you can't!
The bible says,
Romans 8:9 (KJV)
9But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
3Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.
4Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?
5Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
6That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.
7Marvel not that I said unto thee, Ye must be born again.
So why was the Holy Spirit given?
To give us power to be Christ's witnesses - Acts 1:8
To be with us forever - John 14:16
To be our Helper and our Teacher - John 14:26
To baptize us into one body in Christ - I Cor 12:13
To distribute spiritual gifts -I Cor 12:1-11
To seal us - Ephesians 4:30
To bear witness with our spirits that we are God's children - Romans 8:15,16
To continue filling us - Ephesians 4:18
These are just some of the ministries of the Holy Spirit to the believer. I am sure you can list more but the point is that we can not live overcoming lives as Christians without our becoming intimately familiar with the Holy Spirit. We became spiritually alive when we got born again and we are totally powerless without Him. We need to be surrender to Him daily and in constant communication with Him. Only the Holy Spirit can teach us how to live and walk in the Spirit. It is appalling how little is being taught about the spirit-filled life in the churches today. Some have put the Holy Spirit in a closet as if He were a secret. Some are ashamed of Him and afraid that if He really got loose everything would go haywire. Things are going haywire alright but it is because He is being ignored. It is only when we walk in the Spirit that we avoid fulfilling the lust of our sinful flesh.
So if you are wondering why so many believers live such unspiritual lives, well my guess would be that they are perishing for a lack of knowledge of the who the Holy Spirit and what He can do to make their lives full of His fruit. It's all there in the word for anyone that wants to know and all one has to do is ask Him and He will reveal Himself. This is the only way we can be over-comers in this life. It is not only frustrating but totally impossible otherwise.
Luke 11:13 (KJV)
13If ye then, being evil, know how to give good gifts unto your children: how much more shall your heavenly Father give the Holy Spirit to them that ask him?