Christ - our righteousness in both justification and sanctification...

... to be proclaimed perpetually in the church from both the pulpit and the Lord's table by ministers of the gospel.  For the righteousness that comes through faith in Christ is not just the commencement of the Christian life.  It's also the constant ground of our living (Hab. 2:4), the only acceptable righteousness before God.  The only righteousness to be had by even the most holy saint exercised in godly works is the righteousness of God in Christ which comes through faith (Rom 3:21-22).  From John Calvin's Institutes:

We must strongly insist on these two things: That no believer ever performed one work which, if tested by the strict judgment of God, could escape condemnation; and, moreover, that were this granted to be possible (though it is not), yet the act being vitiated and polluted by the sins of which it is certain that the author of it is guilty, it is deprived of its merit. This is the cardinal point of the present discussion. There is no controversy between us and the sounder Schoolmen as to the beginning of justification. They admit that the sinner, freely delivered from condemnation, obtains justification, and that by forgiveness of sins; but under the term justification they comprehend the renovation by which the Spirit forms us anew to the obedience of the Law; and in describing the righteousness of the regenerate man, maintain that being once reconciled to God by means of Christ, he is afterwards deemed righteous by his good works, and is accepted in consideration of them. The Lord, on the contrary, declares, that he imputed Abraham's faith for righteousness, (Romans 4:3) not at the time when he was still a worshipper of idols, but after he had been many years distinguished for holiness. Abraham had long served God with a pure heart, and performed that obedience of the Law which a mortal man is able to perform: yet his righteousness still consisted in faith.  Hence we infer, according to the reasoning of Paul, that it was not of works.  In like manners when the prophet says, "The just shall live by his faith," (Habakkuk 2:4) he is not speaking of the wicked and profane, whom the Lord justifies by converting them to the faith: his discourse is directed to believers, and life is promised to them by faith.   Paul also removes every doubt, when in confirmation of this sentiment he quotes the words of David, "Blessed is he whose transgression is forgiven, whose sin is covered," (Psalm 32:1).  It is certain that David is not speaking of the ungodly but of believers such as he himself was, because he was giving utterance to the feelings of his own mind.   Therefore we must have this blessedness not once only, but must hold it fast during our whole lives.  Moreover, the message of free reconciliation with God is not promulgated for one or two days, but is declared to be perpetual in the Church, (2 Corinthians 5:18, 19).  Hence believers have not even to the end of life any other righteousness than that which is there described. Christ ever remains a Mediator to reconcile the Father to us, and there is a perpetual efficacy in his death, viz., ablution, satisfaction, expiation; in short, perfect obedience, by which all our iniquities are covered. In the Epistle to the Ephesians, Paul says not that the beginning of salvation is of grace, but "by grace are ye saved," "not of works, lest any man should boast," (Ephesians 2:8, 9). (Bk.3.14.11)

WLC-Question 72: What is justifying faith?
Answer: Justifying faith is a saving grace, wrought in the heart of a sinner by the Spirit and Word of God, whereby he, being convinced of his sin and misery, and of the disability in himself and all other creatures to recover him out of his lost condition, not only assents to the truth of the promise of the gospel, but receives and rests upon Christ and his righteousness, therein held forth, for pardon of sin, and for the accepting and accounting of his person righteous in the sight of God for salvation.

HC-Question 61. Why sayest thou, that thou art righteous by faith only?
Answer: Not that I am acceptable to God, on account of the worthiness of my faith; but because only the satisfaction, righteousness, and holiness of Christ, is my righteousness before God; and that I cannot receive and apply the same to myself any other way than by faith only.

HC-Question 62. But why cannot our good works be the whole, or part of our righteousness before God?
Answer: Because, that the righteousness, which can be approved of before the tribunal of God, must be absolutely perfect, and in all respects conformable to the divine law; and also, that our best works in this life are all imperfect and defiled with sin.