One will often hear that one can have "eternal life" in the here and now, and they cannot possibly lose it. This is often based on an appeal to 1 John 5:13 (exegeted here) and John 10:28-29. The latter text reads:
And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand.
One will often hear a phrase from some Protestant that, "if eternal life can be lost, then it is not eternal after all!" Such ignores the fact that "eternal" can often be qualitative, not quantitative; for instance, in his translation of John 17:3, N.T. Wright understands the phrase ζωη ινα to be "life of the age to come." For a book-length discussion of this term in Greek and Hebrew, see Ilaria Ramelli and David Konstan, Terms for Eternity: Aionios and Aidios in Classical and Christian Texts (Piscataway, N.J.: Gorgias Press, 2007). Moreover, such confuses the possession with the possessor. For instance, one can possess a car license, but if one drives recklessly, the one who issued the license can take it away. Indeed, such an absolutist view of John 10:28-29 is refuted by other texts in (1) the Johannine literature, such as John 15:1-6 and (2) the rest of Scripture, such as Heb 6:4-9, where a true believer can lose their salvation. Another example would be one being in a parent's will--one can (using prolepsis) say that they "possess" the inheritance, although its actualisation is still in the future, though it is always possible, due to some heinous action(s), one can be disinherited.
Additionally, as with Rom 8:33-38, the New Testament writers are stating the faithfulness of God and Christ, and how they will not cut people off arbitrarily; further, the biblical authors are emphasising that nothing external to the person will remove them from God's saving love. However, as we know from other texts, a believer can indeed cut themselves off.
In reality, the believer has a down-payment of the Holy Spirit and the ramifications of which will not be seen until the life to come. In 2 Cor 1:22, the apostle Paul writes:
Who hath also sealed us, and given the earnest of the Spirit in our hearts.
This is repeated in 2 Cor 5:5:
Now he that hath wrought us for the selfsame thing is God, who also hath given us the earnest of the Spirit.
The phrase translated as "the earnest" is αρραβων, meaning a deposit/pledge. Notice how it is used in the LXX to denote a down-payment:
And he said, I will send thee a kid from the flock. And she said, Wilt thou give me a pledge (αρραβων), till you send it? And he said, What pledge (αρραβων) shall I give unto thee? And she said, Thy signet, and thy bracelets, and thy staff that is in thine hand. And he gave it her, and came in unto her, and she conceived by him . . . And Judah sent the kid by the hand of his friend the Adullamite, to receive his pledge (αρραβων) from the woman's hand: but he found her not. (Gen 38:17-18, 20)
This meaning of αρραβων also appears in another important soteriological text where Paul is discussing the corporate election of the Church and the αρραβων of those therein:
In whom also we have obtained an inheritance, being predestined according to the purpose of him who worketh all things after the counsel of his own will; that we should be to the praise of his glory, who first trusted in Christ. In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with the holy spirit of promise. Which is the earnest (αρραβων) of our inheritance until the redemption of the purchased possession, unto the praise of his glory. (Eph 1:11-14)
In reality, a believer has great confidence in their obtaining eternal life, which is qualitative (the type of life the Father has, per John 17); however, they only have a “pledge” or “down payment” at this point in time, with the full ramifications of which will not be seen until the life to come (cf. 1 Cor 2:9), predicated upon their being faithful to the end (Phil 2:12)