This means that our knowledge of men can no longer be based on their outward lives (indeed, even though we knew Christ as a man we do not know him like that any longer). For if a man is in Christ he becomes a new person altogether - the past is finished and gone, everything has become fresh and new. All this is God's doing, for he has reconciled us to himself through Jesus Christ; and he has made us agents of the reconciliation. God was in Christ personally reconciling the world to himself - not counting their sins against them - and has commissioned us with the message of reconciliation. We are now Christ's ambassadors, as though God were appealing direct to you through us. As his personal representatives we say, "Make your peace with God." For God caused Christ, who himself knew nothing of sin, actually to be sin for our sakes, so that in Christ we might be made good with the goodness of God.
J.B Phillips Translation 2 Corinthians 5:16-21