St. John Henry Newman described the conscience, which we know as the faculty every human being has to know what is right, as the "aboriginal vicar of Christ in the soul".

The word aboriginal means "first or earliest known, indigenous".

The word vicar means "one serving as a substitute or agent".

But why the association between the conscience and Christ in the soul?

Well, as Christians we're called upon to sacrifice absolutely everything in the pursuit of what's highest—God.

When you sin, you violate that pattern of action / sacrificial relationship, and the conscience calls you out on that violation.

The conscience tells us we're not being sufficiently religious in our sacrifices, sufficiently religious meaning that we're keeping something back from God; we're putting something above Him.

And as we said, being religious in the Christian sense requires you to put nothing above (and sacrifice everything to) God—no matter what.

That's also the very essence of true worship, and that can be seen in the fact that the very first time the word worship is used in the Bible, it's used in reference to Abraham going up the mountain with Isaac to "worship" God.