I am with 1ke 100% – that’s rare if you look through our posts. Children should come second to your spouse, BUT while you and your spouse work harmoniously together: those children will naturally come first. Maybe that doesn’t make sense – and it’s HARD to explain until you are actually there.
OP – I am GLAD you are reading that book. I am REALLY glad you are. It’s a great stepping stone into a marriage, because us women of Western mindset can really sabotage our selves, our husbands, our marriages, our families, our entire lives over undeserved selfishness. I have read it and DH and I were reading “Proper Care and Feeding of Marriage” so your post just reminded us to keep at it. I mentioned it to DH and he agreed.
GOD is number one, but to each of us (DH, myself, and to each one of my children), separately and as a family, he’s PERSONALLY number one. But the personal part of the equation is just THAT: personal. We don’t mention it to each other in a get-in-line kind of way, we just know that God IS God, he is naturally first. In our natural world we have to have proper priorities, and therefor, spouse one, children two, et all. Some people may attack and say “why are your children not first and foremost in your life?” They are, but they are with my DH together. If one of them were sick we would both walk the Earth to make them better…if it came down to my 8yo trying to rule the house through tantrum and playing one against the other: DH wins every single TIME.

You have to experience it to understand what we are saying really.
Good luck with your upcoming wedding, and my suggestion, no matter what you read, is to not come at your fiance with “you are not as important as…” even with GOD. Simply change some wording “Aren’t we so blessed to find each other and create a family in God’s Grace?” He’ll get the message without feeling undermined.
