One of the roles of the Holy Spirit in the preaching of the Gospel is to reprove sinners of their sins unto repentance. To reprove means to convict.
No sinner will become born again without yielding to the conviction by the Holy Ghost. At the new birth, the Holy Ghost baptizes the repentant sinner into the body of Christ. That is, the new birth is by the operation of the Holy Ghost (1 Cor. 12:13; Titus 3:5).
It is when this happens to a sinner that he starts to worship God in spirit (cons. John 4:24; Phil. 3:3). His Christian life will be maintained by the Holy Ghost who makes his communion with the Father and the Son a reality (Rom. 8:26; Eph. 3:16).
It is the Holy Spirit that reveals the secret things of the Father and the Son to the born again Christian, whereby he is able to know God more experimentally (2 Cor. 3:17-18).
Without the Holy Ghost, a believer will not be better than the unbeliever (John 14:26; 1 Cor. 2:13-16; Eph. 3:4-5). Such a believer will be powerless, having no victory over sin and satanic operations.