Pactum Salutis

Some terminology to give an overall understanding to faith and reality:

Pactum Salutis
Historia Salutis
Ordo Salutis

The controlling term of the three would the Pactum Salutis, i.e. it contains the other two, so if one term were to be used for them all it is Pactum Salutis.

Pactum Salutis means Covenant of Redemption.

Historia Salutis means history of redemption (or history of salvation).

Ordo Salutis means order of redemption (or order of salvation).

Just as, if you found yourself stranded in a foreign country, or in some kind of straights in a foreign land, you would appeal to your status as a citizen of Britain or the U.S. or Australia (etc.), and you would get involved with an embassy, and the power that embassy would have to help you would be based on international law, and the law of your nation, etc.; in the same way as an heir of God and not a prisoner of the devil's kingdom it is the Pactum Salutis that secures your status as belonging to God's Kingdom and having the rights of a subject of God's Kingdom. The Covenant of Redemption - Pactum Salutis - was made in eternity between the three Persons of the Godhead (but initiataed by God the Father); carried out in time (Historia Salutis) - effected in time by Jesus and His self-sacrifice; and applied to you by the Holy Spirit via effectual calling and regeneration and justification and sanctification and eventually glorification (Ordo Salutis).

The Pactum Salutis is the eternal Magna Carta, the Constitution, that guarantees your status as a subject of God's Kingdom (as an actual heir of God).

(See vague impressions in all this similar to what stands behind royal rights and charters and standing and so on? It's the language, the reality behind, the constitution of, the eternal royal kingdom. The symbols, the honor and loyalty, the hierarchy, etc., etc., you can see impressions of it all in life here and also in various types of literature, Grail/Athurian literature but also motifs in fantasy genres). Yet it is real when you are called and regenerated and you convert and have saving faith. It is legal standing. That is what justification is. In this world, but also in the spiritual world, where there are forces unfriendly to any who would escape the prison of the Prince of this World, the devil himself...)

If confronted and challenged by the Devil regarding who you belong to you reference the Pactum Salutis. "Pactum salutis, Mr. Devil." And the very fact you know of such a thing and can speak of it as you do shows you have been given saving faith and are justified by God. The very fact you are being confronted by the devil shows you are marked by regeneration (those who belong to the devil are tame slaves and need not be confronted by the devil). Then you draw your sword if Mr. Devil is slow to make way for an heir of the Living God of all Creation...