He gives spiritual life to dead sinners. His work is the work of regeneration. No man can be saved until this work of the Holy Spirit is applied to his heart and will. The unsaved man who has not been born again, or regenerated by the Holy Spirit, does not, and cannot receive the things of the Spirit of God. In fact, he cannot know these things for they are spiritually discerned.
Spiritual truth is utter foolishness to the unsaved man.
John here calls Him the Spirit Of Truth and He says He will guide us into all truth. The Holy Spirit will not exalt or glorify Himself, but He shall receive the things of Christ and show them to us. He will give Christ all the glory. Christ is the Saviour. We preach Christ and His glorious gospel of grace and the Holy Spirit takes this message of the death, burial and resurrection of Christ and applies these truths to the hearts of dead sinners that they might believe on Christ and have everlasting life.