Understanding the continuity between the priesthood of old and the (all-male) Christian priesthood requires anthropological perspective.
"Priesthood" is an interesting subject. The RC argument is based on tradition and their interpretation of scripture. It's all about the interpretation. The following are a few scriptures on priesthood. Read these passages in context. Ask yourself, who are the "us" and "you" being spoken to in these scriptures? Are they only "ordained priests" - or are they all Christians hearing letters written to the churches? You decide.
"And from Jesus Christ, who is the faithful witness, and the first begotten of the dead, and the prince of the kings of the earth. Unto him that loved us, and washed us from our sins in his own blood, 6 And hath made us kings and priests unto God and his Father." Rev 1:5-6
"But you are a chosen people, a royal priesthood, a holy nation, God’s special possession, that you may declare the praises of him who called you out of darkness into his wonderful light." 1 Peter 2:9