God is righteous and heaven is for the righteousness; therefore everybody in heaven must be righteous. Under the law people had to be righteous to enter paradise. Under Grace, people still have to be righteous to enter heaven. There is no change. In fact Jesus said except your righteousness exceeds the righteousness of the Pharisees you could never enter the kingdom of heaven.
The only thing that has changed is how we become righteous; how it is obtained. We can now be righteous before God by faith. It is not a lesser righteousness, but a different means to being right before God.
Jesus is the righteousness of God and if you have Jesus you have righteousness. God demonstrate at the present time His righteousness, that He might be just and the justifier of the one who has faith in Jesus. Rom 3:26
God is not indifferent to sin in fact He is holy and must condemn sin. This is the reason Jesus was punished for our unrighteousness. Now our faith in the Savior is accounted for righteousness. Our faith justifies us – or declares us to be as if we had never sinned.
Friend, it doesn’t mean we are righteous in our self nor is it legal fiction where God says we are righteousness when we are not. But we are actually righteous in Christ or because Christ is within us, we truly are righteous.