Imputed righteousness is the Biblical doctrine of receiving the right standing of Jesus transferred to us when we trust in Him for salvation.  It means that our sins aren’t just forgiven and transferred to Christ, but the merit of His goodness is given to us as well (referred to as double imputation).  It concept is overwhelming and amazing, so it may take much mediation to understand its implications.  To help you think through the importance of the doctrine the following resources are helpful.  They’re ordered them from the quick fly over of the topic to more in depth study

Sinclair Ferguson’s summary of the imputed righteousness (3 minutes)

RC Sproul’s explanation of receiving Christ’s righteousness (5 minutes)

For more extensive study see:

• David Linden treats the topic helpfully in his paper The Very Serious Matter of Imputed Righteousness
• Thomas Brook’s study of the topic of double imputation
• John Piper’s book Counted Righteous for Christ

Additional resources can be found at Monergism