Was Melchizedek a legitimate and real priest of G-d or not?
Yes he was. When I think Melchisedech... I think sacrifice, a "clean oblation" as per the OT prophet Malachais 1:11. The "clean oblation" he offered in thanksgiving to God was bread and wine.
The OT is full of references to sacrifices as prescribed by God Himself. It's an offering to God of some sanctified object made by a legitimate priest.
That reminds me, Lula, any word yet on how Catholic Priests are priests in the order of Melchisedek when you also told us that Judaism (and not Melchizedek's pre-Mosaic religion) was the first divine and priestly religion?
In Psalm 109 King Davod prophesied of Christ, "thou art a priest forever according to the order of Melchisedech." St.Paul applied the same words to Christ in Hebrews 5:6. Again Melchisedech offered a sacrfice of bread and wine. So according "to the order of Melchisedech" means the priesthood of Christ would be like that of Melchisedech. His sacrfice must be of bread and wine.
In verses 10-11, Malachais speaks of the sacrfice of the New Covenant (Law). "I have no pleasure in you (priests of Jewry), saith the Lord of Hosts, and I will not receive a gift of your hand. For from the rising of the sun even to the going down, my name is great among the Gentiles and in every place there is sacrifice and there is offered to My name a clean oblation."
So, at the time of Christ's death on the Cross and the Temple Veil was rent into from top to bottom, clearly and definitely the sacrifice of the Old Law is rejected by God, and its place is to be taken by a clean (unbloody) sacrifice offered universally (from the rising of the sun to its going down) by the Gentiles. The Sacrifice of the New Covenant is to consist of an unbloody offering to God under the rite of bread and wine by the Gentiles all over the world.
In Scriputre, sacrifice has a special meaning and it must be offered by a priest and presented by him to God alone for and in the name of the people.
So sacrfice was an essential element in Old Covenant Judaism and is in the holy religion of Jesus Christ...New Covenant Christianity and specificlally Catholicism. The New Covenant in the Precious Blood of Christ fulfilled and completed the Old Covenant.
The Apostles as well as the early Fathers of the Chruch used expressions as "sacrifice, oblation, host, offering, victim, altar,and priest in reference to Christ's institution of the Eucharist at the Last Supper on HOly Thursday the day before He died on the Cross.
At the Last Supper holding the bread, Christ said, This is My Body which is given for you....and then holding the cup ...This is the chalice of the New Testament in my blood which shall be shed for you." The meaning is clear, that His Body and Blood were "here and now" being offered for sacrfice eucharistically as on the next day It would be offered physically.
The Holy Eucharist is not only a Sacrament but the One Sacrifice of the New Covenant Law and as a sacrifice we call it the Holy Mass.
The short of it is Jesus Christ is the eternal High Priest of the New Law, in virtue of His Sacrficial death on the Cross. The eucharistic sacrifice according to the rite of Melchisedech fulfilled the prophecy of Malchais was instituted by Christ at the Last Supper. On Calvary, Christ made once and for all the necessary sacrifice of reparation. Christ is a Priest forever and Cathoic priests (by the imposition of hands ---Holy Orders) are merely His agents offering Sacrifice in His Name.