A person does not have to overcome in order to be justified. We are justified by faith (Rom 5:1, Gal 2:16). However, a believer will overcome. If he does not overcome, he indicates that he was never justified. That's how overcoming (what some call perseverance) relates to justification.
"Salvation" in Scripture is often eschatological. "Saved" is talking about ultimate salvation in many instances. So when Mark 16:16 says that he that believes and is baptized shall be saved, it is not talking about justification, salvation at the moment of the reception of Jesus Christ. It is talking about someone who believes and is baptized shall be saved in the end. He will be saved from the Great White Throne Judgment. So if I say that you must overcome in order to be saved, I can be talking about future salvation. That doesn't mean that salvation requires the work of overcoming and overcoming and overcoming, and then if you stop overcoming, then you lose your salvation. No, if you are saved, that is, justified, you will overcome, and then you will be saved. If you don't overcome, you will not be saved. Why? Because you were never justified. Justification will produce overcoming, just like it will produce conforming to the image of the Son (Rom 8:29-30).
"Overcoming" is dealing with apostasy. The overcomer does not apostatize. He does not turn from the faith. It is not saying that he will not sin any longer. He will keep believing. If he doesn't keep believing in the Lord alone for salvation, he never believed in the first place (1 John 2:19, 3:6). Jesus will say unto him, "Depart from me, I never knew you."
Ananias and Sapphira never stopped believing in the Lord. That is why they were chastised. Consider Hebrews 12, the chastisement chapter. Those whom God chastises are His sons. He chastises them because they are saved. He chastises them because they are overcomers. God's killing of Ananias and Sapphira was because they were justified. They didn't stop believing in Him. They sinned against Him and He did kill them for it. Chastisement is part of God's sanctification process for believers. God didn't kill Ananias and Sapphira because they had not overcome. He killed them because they had. Ultimate sanctification or glorification occurs when someone is killed by God. That person immediately becomes like Him (1 John 3:1-3), like we all will when we see Him face to face.
I'm concerned about what I see as an attack on a clear doctrine of Scripture that is salvation doctrine. Hopefully it's just a misunderstanding and not an attack. The following are the Lord Jesus speaking:
To him that overcometh will I give to eat of the tree of life, which is in the midst of the paradise of God. Revelation 2:7.
He that overcometh shall not be hurt of the second death. Revelation 2:11.
To him that overcometh will I give to eat of the hidden manna, and will give him a white stone, and in the stone a new name written, which no man knoweth saving he that receiveth it. Revelation 2:17.
And he that overcometh, and keepeth my works unto the end, to him will I give power over the nations. Revelation 2:26.
He that overcometh, the same shall be clothed in white raiment; and I will not blot out his name out of the book of life, but I will confess his name before my Father, and before his angels. Revelation 3:5.
Him that overcometh will I make a pillar in the temple of my God, and he shall go no more out: and I will write upon him the name of my God, and the name of the city of my God, which is new Jerusalem, which cometh down out of heaven from my God: and I will write upon him my new name. Revelation 3:12.
To him that overcometh will I grant to sit with me in my throne, even as I also overcame, and am set down with my Father in his throne. Revelation 3:21.
He that overcometh shall inherit all things; and I will be his God, and he shall be my son. Revelation 21:7.
Do these above verses tell us that we must overcome in order to be saved? I'll let you answer that question. We get our doctrine from the Bible. We understand what salvation is from the Bible. If the Bible speaks, God speaks. He has spoken. Let's believe what He says.
Overcoming is not a work, but a necessary consequence of someone's justification by faith. God produces overcoming. He works in us both to will to overcome and then to overcome. Believers will overcome. If they don't overcome, they weren't believers, and, therefore, they won't be saved. People who are chastised are saved. They have been justified. God does not chastise unbelievers. So if someone is chastised unto death, he is also necessarily, surely an overcomer.
Somebody who says that the doctrine of "overcoming" is "frontloading works" to the gospel is wrong. He is telling a lie either deceived or on purpose. He is also confusing salvation. That's a very bad thing to do. Someone not overcoming may think he's saved because he doesn't think overcoming is a necessary consequence of saving faith. He will be in for the worst rude awakening. Let's not be the cause of that.