In any religion, a priest is someone with a special right of access to the deity – and hence someone who can act as a mediator between that deity and the ordinary people. But it was God’s intention that all his people should have access to Him – that Israel would be a whole kingdom of priests. That intention was frustrated (temporarily) by Israel’s sin (Exodus 32); direct access to God was therefore restricted to the tribe of Levi, and more specifically to the family of Aaron. The fulfilment of God’s intention had to await the inauguration of the New Covenant – under which all of us can know God personally.
”This is the covenant that I will make with the house of Israel
after that time,” declares the LORD…
“No longer will a man teach his neighbour,
or a man his brother, saying, ‘Know the LORD,’
because they will all know me,
from the least of them to the greatest,” declares the LORD.
“For I will forgive their wickedness
and will remember their sins no more.” (Jeremiah 32:33,34)
Along with privilege goes responsibility. Israel’s priestly calling as God’s special people was to display His holiness to the rest of the world – to be “a light to the nations.” On a smaller scale, Aaron’s descendants were expected to maintain higher standards of purity and holiness than the rest of the people (e.g. Leviticus 21); they were also supposed to teach them about God and about the Law. “For the lips of a priest ought to preserve knowledge, and from his mouth men should seek instruction – because he is the messenger of the LORD Almighty.” (Malachi 2:7)
So how should we understand what it means for us to be “a kingdom and priests”? Unlike the Old Covenant priests, we do not have sacrifices to offer (they have all been abolished by Christ); but we do have responsibilities towards the rest of the world – those people who do not (yet) believe. We should be praying for them, witnessing to them, and living lives that glorify God. Our calling is to be “children without fault in a crooked and depraved generation, in which you shine like stars in the universe as you hold out the word of life.” (Philippians 2:15,16)