Below are several quotes from Ellen White that reveal many things the Holy Spirit does. Notice who the Holy Spirit is that she is referring to EVERY TIME. It is NOT a third god as the Trinity doctrine claims.
The Holy Spirit is the presence and power of the Father manifested through Jesus Christ, His only begotten son. This is not a separate person of the Godhead who is being sent, it is the very life of God coming to us through His Son.
The Holy Spirit Comforts us.
“This refers to the omnipresence of the SPIRIT OF CHRIST, called the COMFORTER.” — (E.G. White, 14MR 179.2)
“Let them study the seventeenth of John, and learn how to pray and how to live the prayer of CHRIST. HE is THE Comforter. He will abide in their hearts, making their joy full.” — (E.G. White, RH, Jan 27, 1903)
The Holy Spirit teaches us and guides us into all truth.
“We cannot be with Christ in person, as were His first disciples, but HE has sent HIS Holy Spirit to guide us into all truth, and through this power we too can bear witness for the Saviour. [John 16:13 quoted]” — (E.G. White, Ms30, June 18, 1900)
“The SPIRIT of TRUTH is the only effectual teacher of divine truth; those who are taught of Him have entered the school of CHRIST. How must God esteem the race, that He gave His Son to die for them, and appoints HIS SPIRIT to be man's teacher and continual guide.” — (E.G. White, ST, Oct 24, 1906)
The Holy Spirit helped the disciples fulfill their official duties in connection with the Church and will do the same for us.
“And when He had said this, He [Christ] breathed on them, and saith unto them, Receive ye the Holy Ghost: ... Before the disciples could fulfill their official duties in connection with the church, CHRIST breathed HIS Spirit upon them.” — (E.G. White, DA, p. 805)
“JESUS is waiting to breathe upon all his disciples, and give them the inspiration of HIS sanctifying SPIRIT, and transfuse the vital influence from HIMSELF to his people.” — (E.G. White, ST, Oct 3, 1892)
“JESUS is seeking to impress upon them the thought that in giving HIS Holy SPIRIT He is giving to them the glory which the Father has given him, that He and his people may be one in God.” — (E.G. White, ST, Oct 3, 1892)
The Holy Spirit helps you resist and overcome sin.
Ellen White called Christ by HIS Spirit the third person and is the ONLY one who can overcome sin in you. She did not mean a literal person of course or all the other quotes here would be lies.
“They have ONE God and ONE Saviour; and ONE Spirit--the Spirit of Christ--is to bring unity into their ranks.” — (E.G. White, 9T 189.3, 1909)
Who did she reveal to be the third? ONE + ONE + ONE = “the Spirit of Christ.”
And so Christ by HIS Spirit is the ONLY one that can helps us resist and overcome sin!
“Sin could be resisted and overcome ONLY through the mighty agency of the third person (Spirit of Christ) of the Godhead,” — (E.G. White, DA, 671.2)
“There is no power in you apart from CHRIST, but it is your privilege to have Christ abiding in your heart by faith, and HE can OVERCOME SIN in you, when you cooperate with His efforts.” — (E.G. White, OHC, 76.5)
“With HIS SPIRIT CHRIST sends a reconciling influence and a power that TAKES away SIN.” — (E.G. White, RH, May 19, 1904)
“JESUS ALONE has power to SAVE FROM SIN, to free from the POWER OF EVIL; and to doubt him who has laid down his life for us, is to grieve and insult the Father,” — (E.G. White, RH, February 10, 1891)
The Holy Spirit represents Christ. And yes, that means His own Spirit represents Himself. It can function like a separate person and is one reason why Ellen White called the SPIRIT OF CHRIST the third person.
“CHRIST has left HIS Holy Spirit to be HIS representative in the world, to give celestial aid to every hungering, thirsting soul.” — (E.G. White, Lt84, Oct 22, 1895)
“The Holy Spirit is the SPIRIT of CHRIST; it is HIS representative. Here is the divine agency that carries conviction to hearts. When the power of His Spirit is revealed through the servants of God, we behold divinity flashing through humanity.” — (E.G. White, 13MR 313.3, 1895)
“CHRIST came to our world, but the world could not endure His purity. He has gone to His Father, but HE has sent HIS Holy Spirit to represent HIM in the world till he shall come again.” — (E.G. White, Ms1, Jan 11, 1897)
“The impartation of the Spirit is the impartation of the life of Christ.” — (E.G. White, DA, 805.3)
“Jesus imbues the believer with his spiritual life, which is the Holy Ghost.” — (E.G. White, 3SP, p. 242)
The Holy Spirit ministers and energizes the Church.
“While JESUS ministers in the sanctuary above, HE is still by HIS SPIRIT the minister of the church on earth. HE is withdrawn from the eye of sense, but HIS parting promise is fulfilled, “Lo, I am with you alway, even unto the end of the world.” Matthew 28:20. While HE delegates HIS power to inferior ministers, HIS energizing presence is still with HIS church.” — (E.G. White, DA, p. 166)
This is just a small example of what could be given but I am sure one gets the idea. We have to know who the Holy Spirit is in order that this work can be done. If we choose the idea of a third god, then we have chosen a creation of Satan rather than the Spirit of the Father and Son.