From the time of John the Baptist, baptism had been connected with repentance “for the forgiveness of sins,” and so this meaning continued within the Christian church (Mark 1:4; Acts 2:38).  The Bible teaches that baptism is a witness of our acceptance of Jesus Christ as Lord and Savior of our lives (Acts 16:30-33).  When we are baptized, we are “buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life” (Rom. 6:4; Col. 2:12, 13).

Christian baptism is always connected to belief in Jesus Christ in whom we are saved (Mark 16:16), and also to the reception of the Holy Spirit (Acts 2:38), which testifies that “we are God’s children” (Rom. 8:9, 14, 16). Through baptism we become part of the body of Christ; the Church (1 Cor. 12:13, 27; Gal. 3:27); we are “loved by God and called to be his holy people” (Rom. 1:7). In fact, having been saved by the blood of Christ, by confessing him by faith, we become God’s “chosen people, a royal priesthood, a holy nation, God’s special possession,” so that we “may declare the praises of him who called [us] out of darkness into his wonderful light” (1 Peter 2:9). 

Because of our confession of faith in Christ through baptism, we experience a conversion (2 Cor. 5:17; John 3:5) and change of status. The apostle says: “Once you were not a people, but now you are the people of God; once you had not received mercy, but now you have received mercy” (1 Peter 2:10; Gal. 6:16). Thus, for the Adventist church, baptism represent the witness door by which repentant believers in Christ enter to become part of the body of Christ; the Church.  

By the way you have posit the question on baptism, it seems you are focused on the act itself, rather than on the confession of faith.  But the act of being baptized has no value whatsoever if not accompanied with a profession of faith in Jesus Christ as Lord and Savior of our lives.  Although important, baptism is only an external sign of a heart confession of Jesus Christ as Lord and Savior of our lives (Rom. 10:9, 10).  The faith in Jesus comes first, then baptism follows as a witness of that faith.  But believing in Christ does separate those who are God’s people from those who are not (John 1:12, 13; 3:18).  

Ellen G. White affirms in all her writings this teaching on baptism. For example, see the following statements:

“Baptism is a most sacred and important ordinance, and there should be a thorough understanding as to its meaning. It means repentance for sin, and the entrance upon a new life in Christ Jesus.” ---Child Guidance, p. 499


“The ordinances of baptism and the Lord’s Supper are two monumental pillars, one without and one within the church. Upon these ordinances Christ has inscribed the name of the true God.

“Christ has made baptism the sign of entrance to His spiritual kingdom. He has made this a positive condition with which all must comply who wish to be acknowledged as under the authority of the Father, the Son, and the Holy Spirit. Before man can find a home in the church, before passing the threshold of God’s spiritual kingdom, he is to receive the impress of the divine name, ‘The Lord Our Righteousness.’ Jeremiah 23:6.

“Baptism is a most solemn renunciation of the world. Those who are baptized in the threefold name of the Father, the Son, and the Holy Spirit, at the very entrance of their Christian life declare publicly that they have forsaken the service of Satan and have become members of the royal family, children of the heavenly King. They have obeyed the command: ‘Come out from among them, and be ye separate, ... and touch not the unclean thing.’ And to them is fulfilled the promise: ‘I will receive you, and will be a Father unto you, and ye shall be My sons and daughters, saith the Lord Almighty.’ 2 Corinthians 6:17, 18.

“The vows which we take upon ourselves in baptism embrace much. In the name of the Father, the Son, and the Holy Spirit we are buried in the likeness of Christ’s death and raised in the likeness of His resurrection, and we are to live a new life. Our life is to be bound up with the life of Christ. Henceforth the believer is to bear in mind that he is dedicated to God, to Christ, and to the Holy Spirit. He is to make all worldly considerations secondary to this new relation. Publicly he has declared that he will no longer live in pride and self-indulgence. He is no longer to live a careless, indifferent life. He has made a covenant with God. He has died to the world. He is to live to the Lord, to use for Him all his entrusted capabilities, never losing the realization that he bears God’s signature, that he is a subject of Christ’s kingdom, a partaker of the divine nature. He is to surrender to God all that he is and all that he has, employing all his gifts to His name’s glory.” ---Counsels for the Church, p. 295


“We are not to think that as soon as we are baptized we are ready to graduate from the school of Christ. When we have accepted Christ, and in the name of the Father, and of the Son, and of the Holy Spirit have pledged ourselves to serve God, the Father, Christ, and the Holy Spirit—the three dignitaries and powers of heaven—pledge themselves that every facility shall be given to us if we carry out our baptismal vows to ‘come out from among them, and be ... separate, ... and touch not the unclean thing.’ When we are true to our vows, He says, ‘I will receive you.’”

--- Ms85-1901 (August 30, 1901)