These verses are similar to Proverbs 21:16: "A man who wanders from the way of understanding will rest in the assembly of the dead." The person who is neglecting his salvation is not deliberately setting his mind to turn away from God or His way of life. He is simply, through neglect, allowing himself to drift in that direction. He does not plan to go that way; he gets distracted by things in his life—by hobbies, work, rearing children, and a great many other things. No matter what it is, he allows himself to neglect what has been given to him.
The metaphor used here is of a boat that has slipped its mooring and is drifting within the harbor. Just drifting with the current.
Both of these verses point to a major problem we see in the end-time church of God. We may call it Laodiceanism, and that is a very nice "tag" to put on it. We can comfortably say the word, but are we aware that a Laodicean is a drifter? A Laodicean is somebody who is hanging on to the best of both possible worlds, as he sees it. He has one foot in the church and one foot in the world, and he does not realize that he is drifting.
This is the kind of person that God says He finds unpalatable—one He will spit out of His mouth (Revelation 3:16).