The Collect for the 23rd Ordinary Sunday was not in any pre-conciliar edition of the Roman Missal, but it was in the 8th-century Gelasian Sacramentary.
Deus, per quem nobis et redemptio venit et praestatur adoptio, filios dilectionis tuae benignus intende, ut in Christo credentibus et vera tribuatur libertas, et hereditas aeterna.
Take note of the lovely chiasms, that is, X or Greek chi shapes represented in the word order when the phrases are stacked: redemptio venit … praestatur adoptio (subject verb … verb subject) and also vera libertas … hereditas aeterna (adjective noun … noun adjective). The two passives make a bridge. This is brilliantly crafted, typically terse, quintessentially, Roman. And the Cross is planted in its core.
In play are ancient Roman legal terms having to do with adoption, freedom or manumission, inheritance, etc. Slaves could be freed by the master placing his hand on them. The head of a family could recognise and adopt whom it pleased him to gather in.
Current ICEL translation (2011): “O God, by whom we are redeemed and receive adoption, look graciously upon your beloved sons and daughters, that those who believe in Christ may receive true freedom and an everlasting inheritance.”
By the fact of our unity with Christ, in His and our common human nature, the way to divine sonship was opened up for us.
Christ is the Father’s Son by nature. We are sons by grace. Before baptism we belonged as slaves in the twisted family of this world and its Prince, our Enemy. By baptism we were freed, removed from that family into the Father’s family, not as slaves, but as adopted children.
Our adoption through grace is “perfect”, completed (adoptio perfecta). Perfecta is from perficio, “bring to conclusion, finish, complete”. God, who is not limited by time, sees the results of every gift of adoption. From our point of view, however, adoption will only be completed when we see Him face to face.
Speaking of perfection, this is a difficult mystery to grasp. We are already sons and daughters in a perfect sonship by adoption. On the other hand, that sonship is not yet completed. We lack an essential component: final perseverance in faith and obedience for the whole course of our lives and, at last, their ratification at death in our particular judgment.
It is through many trials that we come to the perfection of adoption which we now share in an imperfectly perfect way.