I actually did understand it the way you had written it, but in my haste to reply I mixed the quotes around.

So to clarify my last post…The part that I can’t get my own mind around is God’s plan for families as being influenced
in any way by cultural and societal shifts. I can’t read that as being compatible with the fact that God is unchanging, and His laws are unchanging. To me, it seems far more likely that the cultural shift has affected individual couples’ interpretation of God’s will for themselves (again, generally speaking.)
I don’t think anyone here is talking about God’s plan for families
in general being influenced by cultural/societal shifts. At least that’s not what I have meant. I’ve been trying to say that God’s plan for
individual families takes into account the concrete circumstances in which they find themselves. You are correct in saying that there is a danger that modern families can misinterpret God’s will and are apt to mis-apply His laws for their lives–I totally agree (and JP2 says as much in
Familiaris Consortio). But I also think that we can say that God has different plans for each of our lives, a plan in which His laws and His holy will take shape in the “concreteness” of our individual lives.
God, in His infinite wisdom and providence, knows what we need and what our call will be before we are even born. He knows what society will be like as we try to make our way, and my point is that He will both challenge us to overcome our circumstances at some times and in some ways, while at other times and in other ways taking into account those circumstances in His will for our individual lives.
An example would be, perhaps, that God’s plan for a particular family includes three children and no more, because mom develops a dangerous medical condition in the labor and delivery of her third child that would make having any more children dangerous. From our perspective, we can sit and discern and say “yes, this is a serious reason to avoid pregnancy”. But in doing this discernment we are discerning what God’s will is for us–so we say that we think from God’s perspective, His will for our family is to not have any more children for X reason, and we are conforming ourselves to His will, as we are called to live it in this area of our lives. I hope that example helps clarify what I mean…
Having children was, in general, more of a non-negotiable priority for Catholic families 100 years ago than it is now. And then in the Bible, fertility is always seen as a blessing and is never questioned by the individual couples’ based on their life circumstances being “not good enough” to foster children. Instead, they trusted God to provide and take care of them. I just see so much less of that kind of attitude nowadays, both with couples who use ABC and with some who use NFP. Simply trusting God is often seen as being imprudent. I’ve not only seen this trend, I’ve been there myself. I can’t see is as being a positive development in society.
I’m not sure that it was so much a “non-negotiable priority” as it was an unavoidable reality. Everyone had a lot of children 100 years ago, not really only Catholic families.

Honestly, I think we might be putting on a pair of rose-colored glasses if we look at people in the past who had large families and say that they “trusted God to provide and take care of them”. Sometimes there was an honest disposition of trust, but more often I think it was just the situation they found themselves in because of normal fertility and a married couple’s active sex life.
Also, it’s clear to me from studying the teaching of the Church that “trust in God” does not preclude the responsible spacing/postponing of births.
Humanae Vitae and the writings of JP2 teach as much. Many other Christians view birth control as the alternatives of modern methods of birth control on the one hand and total “providentialism” on the other. These are not the alternatives presented to us by the Church, and it is not through a fault of faith that Catholic married couples in the 21st century prayerfully decide to responsibly space or postpone pregnancies. Providentialism with regard to pregnancy is not the only way a Catholic couple can demonstrate or live a life of trust in God.
“Simply trusting God” CAN and often DOES involve the use of NFP to avoid/achieve pregnancy. In the end, we have little control over when pregnancy does or does not occur (infertility has taught me that much…

), but we do have much control over the degree to which we place our hearts and futures in God’s hands, do not worry about tomorrow, and trust that He will provide for us according to His will.