Melchisedech was not Sem: for his genealogy is given in Scripture. (Hebrews vii. 6.); nor God the Son, for they are compared together; nor the Holy Ghost, as some have asserted, but a virtuous Gentile who adored the true God, and was king of Salem, or Jerusalem, and Priest of an order different from that of Aaron, offering in sacrifice bread and wine, a figure of Christ’s sacrifice in the Mass; as the fathers constantly affirm. (Haydock)

See Pererius. St. Jerome, ep. ad Evagrium, says, “Melchisedech offered not bloody victims, but dedicated the sacrament of Christ in bread and wine...a pure sacrifice.” See St. Cyprian ep. 63[62?], ad Cæcil.; St. Augustine, City of God xvi. 22, &c. Many Protestants confess, that this renowned prince of Chanaan, was also a priest; but they will not allow that his sacrifices consisted of bread and wine. In what then? for a true priest must offer some real sacrifice. If Christ, therefore, be a priest for ever according to the order of Melchisedech, whose sacrifice was not bloody, as those of Aaron were, what other sacrifice does he now offer, but that of his own body and blood in the holy Mass, by the ministry of his priests? for he was the priest: this is plainly referred to bringing forth, &c., which shews that word to be sacrificial, as in Judges vi. 18. The Hebrew may be ambiguous. But all know that vau means for as well as and. Thus the English Bible had it, 1552, “for he was the priest.” (Worthington)

If Josephus take notice only of Melchisedech, offering Abram and his men corporal refreshment, we need not wonder; he was a Jewish priest, to whom the order of Melchisedech might not be agreeable. It is not indeed improbable, but Abram might partake of the meat, which had been offered in thanksgiving by Melchisedech; and in this sense his words are true. But there would be no need of observing, that he was a priest on this account; as this was a piece of civility expected from princes on similar occasions. (Deuteronomy xxiii. 4; 2 Kings xvii. 27.) (Haydock)