Hebrews 7:3 - Without father or mother

Hebrews 7:3 (KJV)  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.

This verse is simply saying that Christ as high priest in his ordination was the same as Melchizedek, in that genealogy didn't count. He wasn't a Levite, which was a requirement by the law. This was a special God ordained office. Book of Hebrews chapter 7 is clearly concerned with this...

“For it is clear that our Lord descended from Judah, and in regard to that tribe Moses said nothing about priests” (Heb 7:14).

This has nothing to do with Jesus, or Melchizedeks preexistance before they were born. Read any good commentary, they don't claim this.

The verse is just reconciling the lack of priestly genealogy. To the Jews, they could believe that if Melchizedek could be a priest to Abraham without being a descendant of Aaron, the first priest, then so could Jesus Christ.