The judge in the criminal case of the state vs. Bob Jones said, “The defendant will rise as the charges are read.” Mr. Jones’s attorney stood and motioned for Mr. Jones to stand, but he remained seated.
The judge then asked, "Mr. Jones, are you the defendant in this case?"
"No sir, your honor, sir," replied Bob, "I’ve got a lawyer to do the defendin’. I’m just the guy who done it."
Just as Mr. Jones had an attorney who represented him before the judge and spoke on his behalf, so too all of us O.T. people and N.T. people need a representative to speak for us before the Judge.
The priest in the O.T. (in this case Aaron) did something similar in the presence of God. He represented the people before God (the Judge) and spoke to God on their behalf.
For the N.T. Christian we also have a High Priest (Jesus Christ) who is our defendant, since we also are “just the guy who done it (broke the law)”. Christ represents us and speaks for us before God the Father.