Psalm 119:105 "Your word is a lamp to my feet and a light to my path."
If we walk contrary to His word and if we don't follow His word we could easily fall off of His path.
If we stray to far......
2 Thessalonians 2:10-12 "And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved. And for this cause God shall send them strong delusion, that they should believe a lie: That they all might be damned who believed not the truth, but had pleasure in unrighteousness."
I would suggest that the passage to which you refer is speaking of the Tribulation. Those who have rejected the gospel will, during the Tribulation, not be given opportunity to be saved. Those who have already received the Gospel will have been rescued from this Tribulation by rapture previously.