There are quite a number of passages in Paul’s epistles making it clear that everyone will eventually experience salvation, but there’s one verse in particular that really stands out to me as definitive proof that everyone has been saved (from an absolute/ontological perspective): “in whom ye also, having heard the word of the truth — the good news of your salvation — in whom also having believed, ye were sealed with the Holy Spirit of the promise” – Ephesians 1:13
At first glance this won’t seem like proof of the salvation of all to the average person, but if you take some time to really read the verse carefully, it suddenly becomes clear.
If you still don’t see it, that’s okay; I’ll explain it shortly. I should say, it does help to read it in the context of the whole chapter (or at least the section of the chapter it’s a part of), and to also be familiar with the difference between the various types of salvation mentioned in Scripture (if you aren’t already familiar with the different types of scriptural salvation, it’s important you read that linked article before proceeding with the rest of this post in order to understand what I’m going to be getting at). This section of the chapter (verses 3 through 14) is primarily about the blessings that God has purposed beforehand to lavish upon those whom He chose to become members of the body of Christ. Simply put, this section of the chapter is all about how God has predestined certain people to experience certain blessings in Christ, blessings that not everyone will experience. This isn’t Calvinism, however, since experiencing the blessings mentioned in this chapter aren’t about the ontological and eschatological salvations that everyone gets. Those who have been saved from a relative perspective (the people that Paul is writing to, specifically the body of Christ) are those who are “especially saved” (this refers to a special, relative salvation, which means getting to experience extra blessings on top of the salvation that everyone eventually gets to experience), but God is still the Saviour of all mankind.
So what it is that most people miss when they read this verse in Ephesians? Well, what is it Paul is saying happened in this verse? He simply said that his readers had heard the word of the truth, and, in a parenthetical (which is normally placed between commas or em dashes in most Bible versions), said what the word of the truth is: the good news (or gospel, or evangel) of their salvation. Now, by definition, a gospel is a proclamation of good news, not a proposition of how something could be good news if they do the right thing (to be clear, it can include a proposition — if the speaker or writer intends there to be one — but without an included proposition in the text, it remains simply a proclamation of what is rather than what could be).
To put it simply, Paul wrote here that the good news they had heard was the good news of their salvation, not the good news of how they could have salvation if they did something specific (even if that something specific was as simple as choosing to believe the right thing or to have faith in the right Person). The point here is that, because there is no included proposition in the text, the good news they heard was that they already had salvation (which, as we know from his other writings, is the outcome of the good news/gospel he preached, which is that Christ died for our sins, that He was entombed, and that He was roused the third day) prior to hearing about it. Simply put, Paul couldn’t tell them about their already existing salvation if it wasn’t already existing.
Now, most people read this verse and assume that the last part of the verse (“in whom also having believed, ye were sealed with the Holy Spirit of the promise”) actually is a proposition about their salvation, and that they didn’t receive their salvation until they actually believed the good news about said salvation. But this is a misunderstanding due to not being aware of the different types of salvation mentioned in Scripture and assuming there’s only one type of salvation referred to in the entire Bible. All this part of the verse is telling us is that, after they believed in their already existing (absolute/ontological) salvation, they were then sealed with the Holy Spirit of promise (which is a part of their relative/noological salvation, “an earnest of the enjoyment of our allotment, to the deliverance of that which has been procured”).
All that is to say, Paul’s little parenthetical in Ephesians 1:13 is simply that the good news of your salvation was already a fact before they heard it, and if you’re someone who has come to believe in our (all of humanity’s) salvation because of what Christ accomplished (and truly understand what that means), you’re also one of those people who have been predestined beforehand for all the additional blessings Paul mentioned in this chapter as well, and are a member of the body of Christ.
[Postscript: I should note that Calvinists can technically also try to use this verse from a similar perspective, by saying that “the good news of your salvation” is indeed preexistent, but only for the elect under their soteriological system. However, this verse can’t actually work with their doctrine of limited atonement (which is the idea that the elect, under their system, are the only ones that Christ’s death for our sins, and subsequent entombment and resurrection, are efficacious for) because if Paul taught them about their already existing salvation, he couldn’t possibly have known which members of his audience were actually among the elect at the time he told them about this existing salvation, so this interpretation really only works from a “Universalist” perspective.]