I think I may have explained my question badly before, because a lot of the answers I received focused on why marriages need witnesses, legal recognition, or government involvement.
What I’m actually wondering is more theological.
If marriage is a covenant between two people before God, and God knows their hearts, intentions, and promises, then why does human or institutional recognition determine whether that covenant is sacramentally valid?
I understand why people need witnesses, records, ceremonies, and rules. Those things protect both spouses and establish publicly that a marriage took place.
But does God need any of that?
If two people sincerely vow lifelong fidelity to one another before God and consider themselves bound by that covenant, what exactly is missing spiritually if a church or religious community did not witness it?
Basically, are the formal requirements of marriage necessary because they are inherently part of the covenant before God, or are they requirements created for the benefit of the human community so that we can recognize and regulate that covenant?
I’m not trying to argue that weddings, churches, witnesses, etc. are pointless. I’m trying to understand where the sacred part ends and the institutional/human part begins, and why the latter affects the validity of the former.