MELCHISEDEC IS PRIEST OF THE MOST HIGH GOD

HEB 7 V 1

For this Melchisedec, king of Salem, priest of the most high God, who met Abraham returning from the slaughter of the kings, and blessed him;

Jesus Christ is High Priest in the Melchisedec Priesthood.

HEB 6 V 20

20Whither the forerunner is for us entered, even Jesus, made an high priest for ever after the order of Melchisedec.

Now lets look at Heb 7 v 3

Heb 7:3  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. 

Without father without mother...

Melchisedec was a created angel, he did not have a mother or father. Jesus had physical parents, in His physical life and before that He was born of God the Father, before creation, therefore Christ had a Father. 

Without descent...

Melchisedec was a created being, angels neither marry nor are given in marriage,therefore they do not reproduce and therefore do not have descendants. 

Jesus had physical descent. Matt 1 v 1 shows the generations of Jesus Christ, the son of David, the son of Abraham.

Having neither beginning of days...

Days were created in creation week. Beginning of days occurs at a physical birth. Jesus had a physical birth.

HEB 7 V 3

3Without 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.

GEN 1 V 5

And God called the light Day, and the darkness He called Night. And the evening and the morning were the first day.

Nor end of life

Jesus had end of life. Melchisedec has not died.

Made like unto the son of God

Melchisedec is similar to Christ, He is not Christ. Christ is similar to the Father, but He is not the Father.

HEB 7 V 15 
15And it is yet far more evident: for that after the similitude of Melchisedec there ariseth another priest,

Notice this verse: There arises another priest after the similitude of Melchisedec.

Note that carefully, ANOTHER Priest LIKE Melchisedec, that means He is like Melchisedec but definitely not Melchisedec.

Melchisedec is a created being, God created him and gave him a priesthood and eternal life.

Jesus Christ is not created, He is the born Son of God, before creation.  Christ is a High Priest in the Melchisedec order. Christ is  senior to Melchisedec.