You seem to be reinterpreting Jesus's words to suit what you want to believe. In the passage I quoted, Jesus clearly says that only a few find salvation. The problem with any quote from John, is why are the other three gospel writers completely unaware of these statements? It's as if a completely different Jesus were talking.

The writer of Hebrews is using the same language as Paul in 1 Corinthians 3:2: “I gave you milk, not solid food, for you were not yet ready for it. Indeed, you are still not ready”. I don't see why you say it is clearly referring to sanctification. It seems rather that certain followers are not mature enough, not ready to receive the true teachings. How can they be saved?