But this man, because he continueth ever , hath an unchangeable priesthood.
7:25 Wherefore he is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them.
7:26 For such an high priest became us, who is holy, harmless, undefiled, separate from sinners, and made higher than the heavens;
7:27 Who needeth not daily , as those high priests, to offer up sacrifice, first for his own sins, and then for the people's: for this he did once, when he offered up himself.
7:28 For the law maketh men high priests which have infirmity; but the word of the oath, which was since the law, maketh the Son, who is consecrated for evermore.
Nothing in Hebrew 7 indicates that Blessed Virgin Mary is not Christ's mother or that we do not know Christ through her only. He did not have two mothers.
If you are curious why Leo XIII said that, perhaps you should read what he said because I am sure he articulated it better than I can. In fact, I will appreciate a link or a full quote with context if you have it as well.