I once heard John Piper's sermon in which he argued that a believer is being saved by the Gospel. I hope I remember properly, but as I remember, what he meant was that a believer is not only saved by the Gospel, that is, by hearing it and being converted, but also they are being saved by the Gospel, that is, after the conversion, the believer needs to hear the Gospel over and over again and in so doing, the Gospel will keep the believer continue to believe until he gets to Heaven.
I think that is right, but we often forget what we know, even the most important thing as the Gospel truths, hence the need to hear the Gospel over and over again and be encouraged, corrected, healed, rebuked, and most of all, by seeing Jesus again, we can trust Him despite all circumstances.
John Piper also seems to say the same.
PS. Oh, correct me if I got this wrong please.