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?