May I be permitted one small "Arrggghhhhhh!" of frustration?
The teaching is NOT that God simply declared Mary to be free from sin. It is because of the "merits" of Christ:
Declaramus, pronuntiamus et definimus doctrinam quae tenet beatissimam Virginem Mariam in primo instanti suae conceptionis fuisse singulari Omnipotentis Dei gratia et privilegio, intuitu meritorum Christi Jesu Salvatoris humani generis,...I THINK that once again, the hurdle is not only about the Gospel but about "time and eternity." We think that it is "self-evident" (clearly not in the sense of "obvious") that eternity is something which may contain temporality but which is outside of it, in such a way that all times may be said to be "now" in eternity.
"We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Savior of the human race, ...
SO we are not bound to think that the effects of Calvary and of the work of Christ generally are bound to happen only "afterwards."
ANd because of the hypostatic union, we think that the sacrifice of Calvary is both in time and in eternity. So that its effects especially may ripple in every direction in time, not just forward.
Sure from OUR temporal point of view, the conception of Mary was 'before' all the "work" of the Incarnate Christ. But to the One to whom all times are "Now", what does "before" mean?
As always, this is not meant to persuade. I would, I think, pose the problem the same way even if I weren't Catholic. I'm just trying to present the shape of the argument and why, in light of that shape, your objection doesn't address the question.
Who said all times are 'Now' to God...Did he create the world today??? Was the crucifixion today??? How about the resurrection??? Today???
Deu 2:10 The Emims dwelt therein in times past, a people great, and many, and tall, as the Anakims;
Deu 2:11 Which also were accounted giants, as the Anakims; but the Moabites call them Emims.
Do we still have giants today???
How many times has God said thou shalt (future) or thous hast (past)???
Certainly Eternity is timeless but there is no indication that God does not do things in 'time'...I'm sure 'before' means to God the same as it means to us...
And, if the Wedding that makes the church the Bride had taken place in the past (which it hasn't, it's future), there's no place for future so called Christians to be in the Wedding...No current Bride of Christ...
There was no 'ripple' effect for those in prison (Abraham's Bosom)...Jesus had to go there and witness to those folks personally...
Not all those in heaven will be the Bride of Christ...The parables show us that there will be friends and guests at the Wedding as well as the Bride and Groom...
What happened before the Cross is not the same that happens after the Cross...