Although we screwed up, God provided His righteousness via Jesus and offers justification for those who believe in Jesus as Lord and Savior. But justification isn't the only thing we get from Jesus.
Because of the justification, we can get "peace with God through our Lord Jesus Christ" (5:1). Thanks to Jesus's reconciliation plan, our sins will ultimately not separate us from God. This basically means we can have fellowship with God. In particular, we also "have access by faith into this grace in which we stand" (5:2). Grace is basically unmerited favor, which is a fitting description for Jesus who offered himself even though we failed to meet the standards.
And from God's favor and reconciliation with us, we can "rejoice in hope of the glory of God" (5:2). The provisions Jesus provided, like justification and peace and grace, is part of the reason why Jesus is considered a sense of joy for many Christians.