Can a Roman Catholic know that they have eternal life? [duplicate]

Question

If we receive the witness of men, the witness of God is greater: for this is the witness of God which he hath testified of his Son. He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son. And this is the record, that God hath given to us eternal life, and this life is in his Son. He that hath the Son hath life; and he that hath not the Son of God hath not life. These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God. - 1 John 5:9-13

The emboldened word "that you may know" is a word that properly deals with seeing. As used throughout the New Testament in this form it means a past-tense seeing which results in a present-tense knowing ("I saw" means "I know"). The tense here is active so it is the "you" that John has written to who may see unto knowledge.

The emboldened word "have" is present, active, indicative which means that it actually, actively is in the now by the subject and it means:

The verb εχω (echo) means to have or hold and occurs in its various forms 708 times in the New Testament; see full concordance. Its usage slightly transcends that of the English equivalent. Where our English verb "to have" mostly emphasizes possession and control of external things, our Greek verb mostly describes the set of features that collectively define identity. When someone "has" something (say: an object or property, a quality or condition, a word to say, a feeling, a skill, an obligation or conviction), that something helps to determine who that person is, what his past might have looked like, and what his future might be all about. - abarim publications

Can a Roman Catholic say that they know in this sense that, having seen something, they now actually and actively possess knowledge that they have eternal life in a manner that helps define who they are?

Answer 1

Pope Benedict XVI wrote in the first article of his encyclical Spe Salvi.

“SPE SALVI facti sumus”—in hope we were saved, says Saint Paul to the Romans, and likewise to us (Rom 8:24). According to the Christian faith, “redemption”—salvation—is not simply a given. Redemption is offered to us in the sense that we have been given hope, trustworthy hope, by virtue of which we can face our present: the present, even if it is arduous, can be lived and accepted if it leads towards a goal, if we can be sure of this goal, and if this goal is great enough to justify the effort of the journey. Now the question immediately arises: what sort of hope could ever justify the statement that, on the basis of that hope and simply because it exists, we are redeemed? And what sort of certainty is involved here?

https://www.vatican.va/content/benedict-xvi/en/encyclicals/documents/hf_ben-xvi_enc_20071130_spe-salvi.html

Anyway, I read your question and I immediately thought the title of the encyclical is probably the answer to this question.

Hope is what defines Catholics. It doesn't become the sin of presumption which would attempt to define what God can or can't do as the judge of our souls. But it shouldn't be despair either. Catholics never believe that anyone is too bad to be forgiven.

Catholics define that life within you as the life of grace, sanctifying grace in particular, which is our inheritance when we are made children of God at Baptism. But also actual grace, the grace to do good acts, which comes from works of prayer fasting and almsgiving.

This everlasting life is the same everlasting life that Jesus promised to the Samaritan Woman, the same everlasting life that comes from eating the Body and Blood of Jesus in worthily and in faith. This life of grace within us can be killed or severed (I don't know which is a better metaphor) by gravely sinful acts which is what Catholics call mortal sin.

John immediately after says there's a mortal sin that should be avoided if you want this life in you. So, I'm not going to speak for St. John and I don't know that the Church addresses this exact question in light of a notion of 'assurance', but it seems reasonable that what is important is knowing yourself, believing you can know when you're not mired in mortal sin, and the Church does afford us each this right (unless scandal is involved).