Holding faith, and a good conscience; which some having put away concerning faith have made shipwreck:
"Shipwreck" is the process where a ship either runs aground, or sinks. The word does not mean that the ship ceases to be a ship. It has simply become something that is useless for the intended purpose. The verse above shows that those who "put away" faith and a good conscience, must have possessed them in the first place in order to put them aside. That is, they are the same as Paul - Christians. But they have succumbed to deception, or the flesh, and have become Christians who will not achieve the goal of salvation. The context of the Chapter starts off as the "glorious gospel" (v.11), but the immediate context is "God - KING eternal" (v.17). And if we cover the Chapter designation (for the original texts had no Chapter divisions), the immediate context continues into Chapter 2 as GOD'S GOVERNMENT.
Contemporary Christianity teaches that the GOAL of salvation is to go to heaven. But the Bible teaches that man's GOAL is to (i) be in the image and likeness of God, and (ii) subdue and rule the earth (Gen.1:26-28). The GOAL therefore of salvation is to become co-kings with Christ, or make up God's GOVERNMENT when He sets up His Kingdom on earth as Daniel Chapter 2 predicts. Thus, all Christians are "born again to SEE the Kingdom", and must DO something to ENTER the Kingdom - be obedient by calling for Baptism (Jn.3:3-5). Salvation is SO THAT man is equipped to rule the earth, and do it in the image and likeness of Christ. Many Christians will not achieve the GOAL. They start so well, and then slump back to the old ways. This is SHIPWRECK. They are still Christians, but have stopped executing the INTENDED PURPOSE - to be like Christ, and be future rulers.
I think you know some. I do. And what's more, like Paul, I do not take anything for granted. We could "fall away" anytime. Are we still Christians then? YES. Are we fit for the Kingdom when it comes. NO! A man without conscience will embarrass God.