sin covering explanation

from comment 69 here http://www.calledtocommunion.com/2013/01/holy-church-finding-jesus-as-a-reverted-catholic-a-testimonial-response-to-chris-castaldo/#comment-47048

Sin-covering is one way of describing what takes place at justification, because the guilt and eternal punishment due to all our past sins are removed. Man is a temporal being, and we do not escape from our past merely by its being past. Our past eternally remains our past, our history. Justification does not make those past sins never to have happened. They are covered, as it were, through our union with Christ in His satisfactory sacrifice, by which something more pleasing to God than all our sins are displeasing is offered to the Father. But justification-as-translation does effect an immediate *present* transformation.