I find it weird that within some Christian circles, much is made out of the fact that we are all priests and kings. The point that Paul is making here is that we are all equal. There is no hierarchy in the Christian faith except for one. And that one is our Lord, he is our King, he is our high Priest, he is the forgiver of our sins. Just as all are equal, because all have sinned and fallen short of God’s glory – likewise the free offer of forgiveness is given to all, which again makes us all equal.
For those who make a big deal out of kingship: I would remind you that the Prophet Samuel makes the point that God is displeased with the ancient Israel request for a king and actually punishes them for it with a huge storm which wipes out their wheat harvest. As for me, I am no king! I am but the adopted son of the king, in which he raises us all as equals.
Trinitarian Dance 
I’ve seen that in some ‘churches’ where they try to fill all three ministries from the old Testament – Priest, Prophet and King. I agree – I thought the point was Jesus fulfills all of these offices, and so, they are no longer needed!
Drewe, I was reading 1 Samuel this morning and came across a verse where God reluctantly allowed them a king and rebuked them for it. Within the three roles, God did institute the roles of priests and prophets…but not the king. And the priests were always servants of God and the prophets pointing to Christ.
I think that was the point of ‘king’ – Israel was supposed to be a Theocracy, with God always as their King, and the prophet and priestly offices were to point to that. I could be wrong, but I think there is the office of ‘prophet’ which was singular, but there were also ‘prophets’, as there was the office of Priest (which they called high priest) and then the priests. But yes, much of their trouble came (as prophesied!) because they ‘wanted a king like the nations around us’.