This doesn’t justify Once-saved-always-saved theology. You better prooftext would have been John 10, “no one can snatch you”, but neither passage speaks to the issue on hand.
John 6, moreover, says that unless you receive the Eucharist you cannot be saved, and 1 Cor 11 says you must do so “worthily”. So where does that leave a Protestant?
Nothing will justify it to you, you already have your belief system. It just isn’t based on the bible.