Sinners Justified By Faith Receive the Righteousness of Christ Imputed by God to the Elect

Imputation
Justified sinners are those called by God's grace who, through faith in Christ alone, receive God's imputation to them of the satisfaction of Jesus's atoning death and righteous obedience, which for Christ's sake are accounted - credited - reckoned to them as righteousness for their unqualified pardon and acceptance before God as if really performed by them; not a righteousness infused or worked inherently into them, but imputed to them.

Heidelberg Catechism 60  Although my conscience accuses me that I have grievously sinned against all God's commandments, have never kept any of them, and am still inclined to all evil, yet God, without any merit of my own, out of mere grace, imputes to me the perfect satisfaction, righteousness, and holiness of Christ. He grants these to me as if I had never had nor committed any sin, and as if I myself had accomplished all the obedience which Christ has rendered for me, if only I accept this gift with a believing heart. 

Belgic Confession 22 Jesus Christ, imputing to us all his merits and so many holy works which he has done for us, and in our stead, is our Righteousness.

Westminster Confession of Faith 11.1 Those whom God effectually calls, He also freely justifies; not by infusing righteousness into them, but by pardoning their sins, and by accounting and accepting their persons as righteous; not for any thing wrought in them, or done by them, but for Christ's sake alone; nor by imputing faith itself, the act of believing, or any other evangelical obedience to them, as their righteousness; but by imputing the obedience and satisfaction of Christ unto them. 

Westminster Larger Catechism 71 Although Christ, by his obedience and death, did make a proper, real, and full satisfaction to God's justice in the behalf of them that are justified; yet inasmuch as God accepts the satisfaction from a surety, which he might have demanded of them, and did provide this surety, his own only Son, imputing his righteousness to them, and requiring nothing of them for their justification but faith, which also is his gift, their justification is to them of free grace. 

Westminster Shorter Catechism 33 Justification is an act of God's free grace, wherein he pardons all our sins, and accepts us as righteous in his sight, only for the righteousness of Christ imputed to us, and received by faith alone. 

Article XI Of the Justification of Man We are accounted righteous before God, only for the merit of our Lord and Saviour Jesus Christ by Faith, and not for our own works or deservings; Wherefore, that we are justified by Faith only is a most wholesome Doctrine, and very full of comfort, as more largely is expressed in the Homily of Justification.

Imputation - An Union of Representation...

James Buchanan:

"Take the three cases of Imputation which have been specified, and

compare them with one another. We find, that in two out of the three, a change of moral character is the invariable concomitant or consequent of imputation; for the imputation of Adam’s guilt to his posterity, was connected with their loss of original righteousness and the corruption of their whole nature; and the imputation of Christ’s righteousness to His people is connected, in like manner, with their renewal and sanctification; but we also find that, in the third case, —which is as real and as complete an instance of imputation as either of the other two, —the imputation of our sins to Christ was not connected with any change in His holy character, or with the infusion of any, even the slightest’ taint of moral evil; whence we infer that imputation, so far from consisting in, is not even invariably connected with, the infusion of moral qualities. 

• We find again, that in two out of the three cases, representative, and personal, agency are so clearly distinguished as to make it manifest, that the party to whom anything is imputed is not supposed to have had any active participation in the doing of it: for our sins were really, and in the full sense of the term, imputed to Christ as our substitute, yet He had no share in the commission of them; and His righteousness is, in like manner, imputed to us for our Justification, yet we had no share with Him in ‘finishing the work which the Father had given Him to do.’ 

"—Whence we infer that, in the third case, —that of the imputation of Adam’s guilt to his posterity, —it is so far from being necessary to suppose our personal participation in his act, that such a supposition would go far to destroy the doctrine of Imputation altogether, by setting aside the fundamental distinction between the agency of the representative, and that of those who were represented by him. 

"We find, again, that in all the three cases, imputation, whether of sin or of righteousness, is founded on a federal relation subsisting between one and many, —for Adam was constituted the head and representative of his race, and Christ the substitute and surety of His people; and that this relation may be fitly described as amounting to a union between them, in virtue of which they are regarded and treated as being, in some respects, one; but that this union is not such as to destroy the distinction between their respective personalities, or to confound their several acts: for it is still true, that the representative was personally different from those whom he represented, and that his obedience, or disobedience, was his own act, and not theirs, although it is imputed to them; for ‘a union of representation is not a union of identity.’ ‘No imputation of this kind,’ says Dr. Owen, speaking of the imputation of anything that was not ours antecedently, but that becomes ours simply by being imputed, —‘is to account them, unto whom anything is imputed. to have done the things themselves which are imputed unto them… . This is contrary unto the nature of imputation, which proceeds on no such judgment, but on the contrary, (implies) that we ourselves have done nothing of what is imputed unto us, nor Christ anything of what is imputed unto Him.’"

James Buchanan. The Doctrine of Justification

Christ For Us...

Jesus was obedient unto death - even death on a cross - not to obtain a righteousness for

himself but in order to obtain a righteousness for us.

As the second Adam, Jesus's obedience satisfied the Covenant of Works under which God placed Adam - its penalty sanction and obedience probation - not for himself but in our place for us.

Our obedience to God therefore is not to obtain an acceptable righteousness before God because Christ our Surety already has obtained it for us.

Our obedience therefore is not to satisfy any kind of probationary test of obedience before God because Christ has already passed God's probationary test for us.

Our obedience is not unto or for ourselves in order to satisfy God's Law but offered thankfully unto God and offered to others in love for their benefit, even as Jesus's obedience was not unto himself nor for himself but offered to God in love for us in order to satisfy the requirement of God's holy Law for our benefit.

God's Justification by his free grace through faith in Christ alone removes the necessity of any self-directed or self-enhancing motive of obedience to the purpose of obtaining an acceptance before God for the believer, i.e. to obtain a better or more secure standing before God. Christ alone has completely secured a perfect standing of righteousness before God for us who believe in him. For Christ alone accomplished all of our salvation for us.

Jesus's obedience was not for himself but for others...

Ergo - the disciple not being above the Teacher - our obedience is not offered for the benefit of ourselves in any way but for the benefit of others, offered in thankfulness to God for his free gift of grace in Christ Jesus.

Luke 10:26-28

Romans 5:12-21
Romans 15:1-3
Philippians 2:1-11
Matthew 10:24-25a