Thomas Goodwin makes a great point in his work on Justifying Faith (Works, Vol. 8) where he speaks of Christ justifying us.
He says the Ark of the Covenant is a type of the Person of Christ and the Mercy Seat is a type of God’s grace. I prefer to think of it as a type of the Propitiation of Christ. So the Person and Work of the Son are necessary elements in our being justified. There can be no justification apart from the other. Just as the Ark and the Mercy were joined together, so too is the Person and Work of the Son.

The Works of Thomas Goodwin, Volume 8, Book 2, Chp. 1, p. 141.