"And indeed (to enlarge this a little), as there is the same reason and ground for the one that there is for the other, he being a public person in both, so the rule will hold in all things which God ever doth to us, or for us, which are common with Christ, and were done to him; that in them all Christ was the first-fruits, and they may be said to have done in us, or to us, yea, by us, in him and with him. Whatever God meant to do for us and in us, whatever privelege or benefit he meant to bestow upon us, he did that thing first to Christ, and (some way) bestowed the like on him as a common person, that so it might be by a solemn formal act ratified, and be made sure to be done to us in our persons in due time, having first been done to him representing our persons; and that by this course taken, it might (when done to us) be effected by virtue of what was done to him. Thus God meaning to sanctify us, he sanctifies Christ first, in him as a common person sanctifying us all: 'For their sakes, I sanctify myself, that they also may be sanctified through your truth' (John 17:19). He sanctifies the human nature of Christ personal (that is his body), and him first, as a common person representing us, that so we, being virtually and representatively sanctified in him, may be sure to be sanctified afterwards in our own persons, by means of his sanctification. And so in like manner for our sakes he was 'justified in the Spirit;' because we were to be justified, and so to be justified in him, and with him as a common person." p.81
"we were all justified in Christ when he was justified."
|Dr. Richard Gaffin|
"And further, to confirm and strengthen this notion, because his resurrection was the first moment of this his justification from our sins, therefore it is that God calls it his first begetting of Christ, 'This day I have begotten thee' (Acts 13:33) speaking manifestly of his resurrection. And the reason of his so calling it, is, because all the while before he was covered with sin, and 'the likeness of sinful flesh;' but now, having flung it off, he appears like God's Son indeed, as if newly begotten. And thus also there comes to be the fuller conformity between Christ's justification and ours. For as our justification is at our first being born again, so was Christ also at this first glorious begetting." p.80