We don’t need to know about every person’s eternal destiny. We simply can’t know that. Even early Protestant leader John Calvin held that no one could know for sure if someone else was in the elect or even (absolutely) if they themselves were. But we can believe and know that God is both just and merciful, and that every person will end up where they deserve to be.

We do know that we have to believe that Jesus died for us, and wholeheartedly serve him as our Lord and Savior and Redeemer — as a disciple.

One has to be in a state of grace, and not in a state of mortal sin, in order to be saved in the end. That’s why we Catholics are big on examination of conscience and confession. We’re not “out to sea” without any hope or joy, because we’re not absolutely certain of our salvation. God wants us to be vigilant and to persevere. This is a good thing, not a bad thing, because human beings tend to take things for granted and become complacent.

The degree of moral assurance of salvation we can attain to is very high. The point is to examine ourselves to see if we are mired in serious sin, and to repent of it. If we do that, and know that we are not subjectively guilty of mortal sin, then we can have a joyful assurance that we are on the right road.

I always use my own example by noting that when I was an evangelical Protestant, I felt very assured of salvation, though I also believed (as an Arminian) that one could fall away if one rejected Jesus outright.

Now as a Catholic — these past 34 years — I feel hardly any different than I did as an evangelical. I don’t worry about salvation. I assume that I will go to heaven one day, if I keep serving God. I trust in God’s mercy, and know that if I fall into deep sin, his grace will cause me to repent of it (and I will go along in my own free will) so that I can be restored to a relationship with him.

We observe St. Paul being very confident and not prone to a lack of trust in God at all. He had a robust faith and confidence, yet he still had a sense of the need to persevere and to be vigilant. He didn’t write as if it were a done deal — that he got “saved” one night in Damascus and signed on the dotted line, made an altar call and gave his life to Jesus, saying the Sinner’s Prayer or reciting John 3:16. 

To the contrary, Paul stated that he himself could possibly be “disqualified” (1 Corinthians 9:27) and he warned, “Let anyone who thinks that he stands take heed lest he fall” (1 Corinthians 10:12). He also urged Christians to “stand fast therefore, and do not submit again to a yoke of slavery” (Galatians 5:1), and even chided some of the Galatians, writing: “You are severed from Christ, you who would be justified by the law; you have fallen away from grace” (Galatians 5:4).

Paul uses tentative language about these matters: “If possible I may attain the resurrection from the dead. Not that I have already obtained this … but I press on to make it my own” (Philippians 3:11-12). He casually assumes the possibility of any Christian possibly falling away, or committing apostasy: “Some will depart from the faith” (1 Timothy 4:1); “some have already strayed after Satan” (1 Timothy 5:15).

So we see that the biblical record gives us what is precisely the Catholic position — neither the supposed “absolute assurance” of the evangelical Protestant or Calvinist, nor the legalistic, Pharisaical, mechanical caricature of what outsider, non-experienced critics of Catholicism think Catholicism is, where a person lives a “righteous” life for 70 years, then falls into lust for three seconds, gets hit by a car, and goes to hell (as if either Catholic teaching or God operate in such a superficial fashion).

One can have a very high degree of moral assurance and trust in God’s mercy. St. Paul shows this. He doesn’t appear worried at all about his salvation, but on the other hand, he doesn’t make out that he is absolutely assured of it and has no need of persevering. He can’t “coast.” The only thing a Catholic must absolutely avoid in order to not be damned is a subjective commission of mortal sin that is unrepented of. We have to be vigilant to avoid falling into serious sins that will bar us from heaven (1 Corinthians 6:9-11; Galatians 5:19-21; Ephesians 5:3-6; Revelation 21:8; 22:15). 

But for Paul, vigilance and perseverance are not antithetical to hope and a high degree of assurance and joy in Christ. He refers to “our hope of sharing the glory of God” (Romans 5:2), but doesn’t assert that we are absolutely assured of this salvation at all times, or that we can never lose it. He teaches that we are saved “provided that” we “continue in the faith, stable and steadfast, not shifting from the hope of the gospel” (Colossians 1:23), and that we are “heirs of God and fellow heirs with Christ, provided we suffer with him in order that we may also be glorified with him” (Romans 8:17). It’s not a one-time, instant salvation that can never be lost.

The author of Hebrews echoes Paul’s thought in this respect: “Show the same earnestness in realizing the full assurance of hope until the end” (Hebrews 6:11); “Let us hold fast the confession of our hope without wavering” (Hebrews 10:23).

We see, then, that Holy Scripture backs up Catholic claims at every turn. We have a very strong assurance and faith and hope, yet this is understood within a realistic paradigm of perseverance and constant vigilance in avoiding sin, that could potentially lead us to damnation.