Good question! Here are two more questions to think about as well: If Christians have already been made the righteousness of God in Christ Jesus here on earth, then we need to ask ourselves: “Why don’t believers demonstrate His righteousness in all we do?” And why would Jesus tell us to seek first His Kingdom and His righteousness, if we already embody that reality (Matthew 6:33)?
Possibly the best way to answer this question is for you to know that all the Scriptures that contain “in Christ” are heavenly positions that we have access to when we first believe that Jesus came in the flesh and the Father raised Him from the dead. This is an incredible and wonderful reality! The LORD of LOVE also gives us an initial deposit of Himself (see below) here on earth, and it is our job (as good stewards) to grow that initial deposit, so that we can become (be made into) the exact same image as Yeshua. As I mentioned previously, the maturation steps for becoming holy, as He is holy are:  salvation  sanctification  purification. The process of fully becoming (i.e. manifesting on earth) the heavenly position fully paid for on the cross, which is the righteousness of God in Christ Jesus, belongs in the purification stage of a believer’s walk. This is not always a clear-cut process, and sometimes our sanctification will bleed over into our purification. Another series of three to consider in all this is:  obedience leads to  righteousness, which leads to  holiness (Romans 6:16,19).
The verse about “righteousness” that Christendom tends to name and claim without realizing its full potential here on earth is 2 Corinthians 5:21. You’ve heard it touted, and it is a good and proper foundation that we all need to begin with: “I am the righteousness of God in Christ Jesus.” However, this verse does not say what’s being touted. It says: “For He made Him who knew no sin to be sin for us, that WE MIGHT BECOME THE RIGHTEOUSNESS OF GOD IN HIM (2 Corinthians 5:21 NKJV). The Greek verb for “might become” means to begin to be, to come upon a new stage in life, or the process of becoming (to undergo change or development).
Additionally, it is very helpful to understand “FULLNESS” in Scripture. Here are some previous posts about the concept of FULLNESS and the initial 10% DEPOSIT OF THE HOLY SPIRIT we receive when we accepted Jesus Christ as our Lord and Savior:
 “FULLNESS DEPOSIT” posted on August 21, 2013: http://wp.me/p2k1dQ-ap
 “FULLNESS IS A 10 % DEPOSIT UNTIL…” Posted September 2, 2013: http://wp.me/p2k1dQ-aO
The divine Melchizedek/Bridal journey will cause the 10% tithe of the Holy Spirit within His holy blood-bought vessels to grow in amount, magnitude, and degree to the fullness of the measure of the stature of Christ, as led by the Spirit of God according to the perfect will of the Father.
Romans 14:17 tells us that “THE KINGDOM OF GOD IS … RIGHTEOUSNESS AND PEACE AND JOY IN THE HOLY SPIRIT.” These three are spiritual dimensions within a person that the Lord seeks to grow within His Kingdom vessels. Remember how the STM Nov 20th post spoke about a DEEP RED mystery of His Kingdom that will be realized by His Crucified Ones (i.e., mature sons)? They will return to their primordial position where their body will be clothed in righteousness, their soul will be completely filled with the shekinah glory of God where it’s the permanent Dwelling Place of God (which is the fullness of the Seven Spirits of God as well as the Nature of Christ), and their spirit will be in constant communion with their Creator? (Refer to http://wp.me/p2k1dQ-jR) Know that one’s body can not be fully clothed with righteousness “UNTIL THE REDEMPTION OF THE PURCHASED POSSESSION (Ephesians 1:14), which from my studies I believe is the filling up of the soul of a person with the 100% fullness of the Seven Spirits of God, which is how Jesus walked in the nature of Christ on earth.
To Him be the Glory & may we first seek His Kingdom and His righteousness!
~ Robin Main