So far as I am aware, this basic concept was first expressed in a manner similar to this by Abraham Kuyper.
God established three societal institutions: family, church, and state. Each of these three institutions have sovereignty (under God) over their own sphere (or jurisdiction). They inevitably overlap, but if the leaders of one sphere attempt to exert authority over another sphere, that is tyranny. As I read it, the 1st Amendment says nothing more than that the State has no jurisdiction over the Church. In matters of civil government the Church must heed the State’s authority, and in matters of religion the State must heed the Church’s authority.
Legislation is the act of applying a morality to governmental issues. Morality is the application of a god’s character to human affairs. How God’s character applies to matters of state is somewhat different than how God’s character applies to matters of religion and family. All law is contextual and cannot be discerned correctly if torn from the situation of its application.
If a YHWH-worshiper sacrificed to an idol this was worthy of the death penalty (“church sphere”); if a Moabite did so the same did not apply. If the Moabite became a sojourner with Israel, however, in that case, “For the [religious] assembly”, there shall be one statute for you and for the stranger who sojourns with you….” (Numbers 15:15)
Now, in the scope of time, God will hold the “Moabite” responsible for not worshiping Him, but that is God’s prerogative, not ours.
How do we know this was relative to the religious assembly? Context. The entire chapter is about worship regulations, and the immediately preceding sentence says, “And if a stranger is sojourning with you, or anyone is living permanently among you, and he wishes to offer a food offering, with a pleasing aroma to the Lord, he shall do as you do.”
So Ruth the Moabitess was constrained by this passage, but her sister, Orpah, was not.