All we like sheep have gone astray; we have turned—every one—to his own way; and the LORD has laid on him the iniquity of us all. —Isaiah 53:6
What does it mean that the Lord has laid on Jesus the iniquity of us all? We are, indeed, forgiven our sins. We also have the righteousness of Christ standing as our own. But it’s even more that that: By faith we are united to Christ.
John Calvin writes,
Therefore, that joining together of Head and members, that indwelling of Christ in our hearts—in short, that mystical union—are accorded by us the highest degree of importance, so that Christ, having been made ours, makes us sharers with him in the gifts with which he has been endowed.
We do not, therefore, contemplate him outside ourselves from afar in order that his righteousness may be imputed to us but because we put on Christ and are engrafted into his body—in short, because he deigns to make us one with him. For this reason, we glory that we have fellowship of righteousness with him. (Institutes of the Christian Religion, p. 737)
Jesus’ death for us isn’t impersonal, as if it can be stripped down to a simple formula. He died for us to make us his own, to bring us into the wonders of knowing him and being known by him.