Objection 1. It would seem that Christ's predestination is not the exemplar of ours. For the exemplar exists before the exemplate. But nothing exists before the eternal. Since, therefore, our predestination is eternal, it seems that Christ's predestination is not the exemplar of ours.
Objection 2. Further, the exemplar leads us to knowledge of the exemplate. But there was no need for God to be led from something else to knowledge of our predestination; since it is written (Romans 8:29): "Whom He foreknew, He also predestinated." Therefore Christ's predestination is not the exemplar of ours.
Objection 3. Further, the exemplar is conformed to the exemplate. But Christ's predestination seems to be of a different nature from ours: because we are predestinated to the sonship of adoption, whereas Christ was predestinated "Son of God in power," as is written (Romans 1:4). Therefore His predestination is not the exemplar of ours.
On the contrary, Augustine says (De Praedest. Sanct. xv): "The Saviour Himself, the Mediator of God and men, the Man Christ Jesus is the most splendid light of predestination and grace." Now He is called the light of predestination and grace, inasmuch as our predestination is made manifest by His predestination and grace; and this seems to pertain to the nature of an exemplar. Therefore Christ's predestination is the exemplar of ours.
I answer that, Predestination may be considered in two ways. First, on the part of the act of predestination: and thus Christ's predestination cannot be said to be the exemplar of ours: for in the same way and by the same eternal act God predestinated us and Christ.
Secondly, predestination may be considered on the part of that to which anyone is predestinated, and this is the term and effect of predestination. In this sense Christ's predestination is the exemplar of ours, and this in two ways. First, in respect of the good to which we are predestinated: for He was predestinated to be the natural Son of God, whereas we are predestinated to the adoption of sons, which is a participated likeness of natural sonship. Whence it is written (Romans 8:29): "Whom He foreknew, He also predestinated to be made conformable to the image of His Son." Secondly, in respect of the manner of obtaining this good--that is, by grace. This is most manifest in Christ; because human nature in Him, without any antecedent merits, was united to the Son of God: and of the fulness of His grace we all have received, as it is written (John 1:16).
Reply to Objection 1. This argument considers the aforesaid act of the predestinator.
The same is to be said of the second objection.
Reply to Objection 3. The exemplate need not be conformed to the exemplar in all respects: it is sufficient that it imitate it in some.
Source: Summa Theologica (New Advent)