Newness Of Life
The coming of the Holy Spirit of God into the life of a Christian enables the person to be a Christian (see The Cure For The Carnal Mind):
"8:6 For to be carnally minded is death; but to be spiritually minded is life and peace. 8:7 Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be. 8:8 So then they that are in the flesh cannot please God. 8:9 But 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. 8:10 And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness. 8:11 But if the Spirit of him that raised up Jesus from the dead dwell in you, he that raised up Christ from the dead shall also quicken your mortal bodies by his Spirit that dwelleth in you. " (Romans 8:6-11 KJV)
"Even so we also should walk in newness of life"
The Holy Spirit does something else along with enabling a person to see. It enables them to grow toward being "born again" (see the Fact Finder question below). The Holy Spirit's entry is usually centered around baptism, an act of repentance that itself symbolizes personal acceptance of the sacrifice of Christ and the resurrection to come if one repents.
"6:3 Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? 6:4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. 6:5 For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection: 6:6 Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin." (Romans 6:3-6 KJV)
The coming of the Holy Spirit does not necessarily happen after or at baptism; sometimes it comes before baptism e.g.
"10:44 While Peter yet spake these words, the Holy Ghost fell on all them which heard the word. 10:45 And they of the circumcision which believed were astonished, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Ghost. 10:46 For they heard them speak with tongues, and magnify God. Then answered Peter, 10:47 Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?" (Acts 10:44-47 KJV)
Regardless of when the Holy Spirit is granted, it requires repentance in order for it not to be rejected by the one to whom it is offered.
"2:38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. 2:39 For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call." (Acts 2:38-39 KJV)
Fact Finder: How does the Holy Spirit enable the beginning of a process of development toward a new birth?