St. Thomas Aquinas (see Summa Theo., P.III, Q.I, Art. 3), St. Bonaventure, Bl. John Duns Scotus, and many others asked the question, “If Adam had not sinned would God have become Incarnate?” -They did this NOT as a hypothetical question, but rather because the answer to the question dilineated what the primary motive of the Incarnation was in God’s plan.
If we follow the “yes” crowd who speak of an unconditional Incarnation: St. Maximus the Confessor, Abbott Rupert of Deutz, Bishop Robert Grosseteste, St. Albert the Great, Fr. Alexander Hales, Bl. John Duns Scotus, St. Bernardine of Sienna, St. John of the Cross, St. Francis de Sales, St. Lawrence of Brindisi, Pope Benedict XVI, etc., then one might ask how would Christ have come? In flesh capable of suffering and dying? Incapable of suffering and dying? In a glorious state?
While this is true speculation since we don’t have any immediate knowledge of exactly how the Incarnation would have taken place in a sinless world, nonetheless it seems clear enough that A) Our Lord would not have come in passible flesh since there would have been no need to redeem the human race by suffering and death, B) Our Lord would not, according to the common opinion of the scotistic school, have come in a glorious state because if He did, He would in no way have been able to merit grace and glory for Angels and mankind.
So the Word would have become flesh in an impassible state had Adam not sinned. Thus not in the likeness of sinful flesh, as St. Paul dubs it, nor in a glorified state incapable of merit.
In a recent correspondence I had with my great Professor in Dogmatic Theology, Fr. Peter M. Fehlner, F.I., on how Christ would have merited for us if He did not come in passible flesh, he wrote me that:
Adam and Eve were impassible before they sinned; so were the Angels before completing their trials. But no one thinks they were not in the state of viator and so incapable of meriting.
In addition Christ would have come in the state of viator, even if Adam had not sinned, because Adam still had to be saved (even if not redeemed) by the merits of Christ by way of an impassibilis sacrifice. But in this scenario human salvation is for the sake of the Incarnation, not vice versa, just as creation is for the sake of the Incarnation and not vice versa.
This is the position of the great Scotists especially of the 17th century… The state of Christ’s coming as man had Adam not sinned is always described as impassible, not glorious.
On the theme of salvation vs. redemption according to the mind of St. Irenaeus, one can read more here.