HE is our righteousness! The righteousness we have is HIS righteousness, His very life and nature, put within us!
If our righteousness is from God Himself - and is actually Jesus within us - then we are perfectly righteous!
We may not feel righteous and we may not act righteous. Satan, other people, and even thoughts that come to our mind may say that we are not righteous. But God says we are righteous, the Holy Spirit within testifies we are righteous, and Jesus has given us His own righteousness, so what is left to say? We just stand up and give our testimony: "I am the righteousness of God in Christ Jesus, and nothing can ever change His righteousness in me!" Yes!
"But no weapon that is formed against you shall prosper, and every tongue that shall rise against you in judgment you shall show to be in the wrong. This [peace, righteousness, security, triumph over opposition] is the heritage of the servants of the Lord [those in whom the ideal Servant of the Lord is reproduced]; this is the righteousness or the vindication which they obtain from Me [this is that which I impart to them as their justification], says the Lord." Is. 54:17 (AMP)