( source & reference )
"The doctrine of the Trinity which was established in the church by the council of Nice, A. D. 325. This doctrine destroys the personality of God, and his Son Jesus Christ our Lord. The infamous, measures by which it was forced upon the church which appear upon the pages of ecclesiastical history might well cause every believer in that doctrine to blush." (J. N. Andrews, March 6, 1855, Review & Herald, vol. 6, no. 24, page 185)
"Our knowledge of this remarkable personage is derived only from Genesis 14, Psalm 110, and what Paul has written concerning him in the book of Hebrews. Many things respecting him are purposely concealed by the Holy Spirit, and it would, therefore, be fruitless for us to attempt to bring them to the light. He was king of Salem; he was priest of the most high God; he was, by virtue of his office, even the superior of Abraham; Christ is a priest after his order. He once met Abraham and received tithes of him, and blessed him. This is the substance of our knowledge of Melchisedec. When it is asked whether he was not identical with this or that remarkable man of his time, or when it is inquired of what race he was, and who were his parents, and how long he lived, and when he died, the answer must be, that we are not informed touching these things. But the following language of Paul has given rise to many strange speculations concerning him. Paul says of him that he was "without father, without mother, without descent, having neither beginning of days, nor end of life; but made like unto the Son of God; abideth a priest continually." (Hebrews 7:8)
Now, if these words be taken in an absolute sense, they can be true of no human being. Adam alone, of all the human race, was without father, and without mother, and without descent. But Adam had beginning of days and end of life. Enoch had no end of life, but he had all the other things which Paul says Melchisedec had not. So of Elijah, who, by the way, did not exist till long after the days of Melchisedec. Every member of the human family, except Adam, has had parents, and every one has had beginning of days; and indeed, with two exceptions, everyone has had end of life. Even the angels of God have all had beginning of days, so that they would be as much excluded by this language as the members of the human family. And as to the Son of God, he would be excluded also, for he had God for his Father, and did, at some point in the eternity of the past, have beginning of days. So that if we use Paul's language in an absolute sense, it would be impossible to find but one being in the universe, and that is God the Father, who is without father, or mother, or descent, or beginning of days, or end of life. Yet probably no one for a moment contends that Melchisedec was God the Father. 1. He is called the priest of the most high God. Hebrews 7:1. It is the business of the priest to make offerings to God. He surely did not make offerings to himself. 2. He is called by Paul a man, though greater than Abraham. 3. Paul speaks of him in Hebrews 7:6 as really having descent, though he does not know what it was. 4. Melchisedec in Genesis 14:20 blesses the most high God, a plain evidence that it was not himself he thus blessed. Melchisedec is said to be made like unto the Son of God. But this shows that he is not God the Father; for he is not made like his Son, nor indeed does he have existence derived from another. But the Son is said to be the express image of his Father. Hebrews 1.
What then do the words of Paul in Hebrews 7:8 really signify? We have seen that they cannot be taken in an absolute sense; for they involve us in contradictions and absurdity. But if they are taken in a limited sense, and interpreted according to the manner of speaking that was usual with the Hebrews, we shall find them easy of explanation. The Hebrews kept very exact genealogical registers. Particularly was this the case respecting their priests; for if the priest could not trace his genealogy back to Aaron, he was not allowed to serve in the priesthood. Those who could not show their record in such tables were said to be without father and mother, and without descent. This did not signify that they had no ancestors, but that the record of them was not preserved. This is exactly the case of Melchisedec. He is introduced in Genesis without record of his parentage, the Holy Spirit having purposely omitted that matter. He is said by Paul to have no beginning of days, nor end of life. This does not mean absolutely that there was no beginning of existence with him, for it is only true of one being in the universe, viz., God the Father. But the evident meaning of the apostle is this: that no record of his birth or of his death appears in the history which is given us of him. He appears without any intimation given us of his origin; and the story of this priest of the Most High ends without any record of his death. These things were purposely omitted that he might be used to represent, as perfectly as possible, the priesthood of the Son of God. And so the same Spirit of inspiration that led Moses to withhold these particulars concerning Melchise-dec, did also lead Paul to use that omission to illustrate the priesthood of Christ. We would do well to leave the case of Melchisedec just where the Scriptures leave it." (J. N. Andrews, September 7, 1869, Review & Herald, also found in the January 4, 1881 edition of Review & Herald)
[is this what the SDA pioneers believed?]