Again Christ's resurrection is a validation that Christ's death, putting away our offences, if were elect, that His death justified us. Here's why, when He died He purged us from our sins ! Heb 1:3
3 Who being the brightness of his glory, and the express image of his person, and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high:
His sitting down on the right hand is what He after purging our sins. Now the word purge here is the greek word katharismos and means:
cleansing, purifying, purification, literal, ceremonial, or moral; met: expiation.
a cleansing from the guilt of sins by the expiatory sacrifice of Christ. And because that's so they are Justified. In fact the word for Justification paralells this, its the word dikaiōsis:
), the act of God's declaring men free from guilt and acceptable to him
And that's what Christ's purging us from our sins accomplished . Justification before God ! The resurrection validates it !