I think it depends on the issue at hand.
If a Christian supports the DNC are they supporting evil? Yes. Is it a sin? Yes. Does this mean they are no longer saved? No.
If a Christian cheats on his or her taxes are they disobedient to God? Yes. Is it a sin? Yes. Do they lose their salvation? No.
If Paul did not discipline his body and he forfieted "the prize" woukd he also forfeit his salvation? I do not believe so.
I lean towards
@Van 's view that we are talking about "rewards".
I do not believe this is about earning salvation through works but instead about "laying up treasures in Heaven".
There is a consequence if Paul did not discipline his body and it involves more than the loss of crowns as one can become a castaway.
1 Corinthians 9:24 Know ye not that they which run in a race run all, but one receiveth the prize? So run, that ye may obtain.
25 And every man that striveth for the mastery is temperate in all things. Now they do it to obtain a corruptible crown; but we an incorruptible.
26 I therefore so run, not as uncertainly; so fight I, not as one that beateth the air:
27 But I keep under my body, and bring it into subjection:
lest that by any means, when I have preached to others, I myself should be a castaway.
So that is why running that race by faith in Jesus Christ as our Good Shepherd & Friend to help us to resists sin in thought, word, and deed, in following Him daily is the race to run for that high prize of our calling to be that vessel unto honor in His House to avoid becoming a castaway by living in sin or practicing works of iniquity be it religious works that deny Him or a supernatural phenomenon that denies Him, and not just living the wild life in sin like the prodigal son.
Hebrews 12:1Wherefore seeing we also are compassed about with so great a cloud of witnesses,
let us lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us,
2 Looking unto Jesus the author and finisher of our faith; who for the joy that was set before him endured the cross, despising the shame, and is set down at the right hand of the throne of God.
3 For consider him that endured such contradiction of sinners against himself, lest ye be wearied and faint in your minds.
4
Ye have not yet resisted unto blood, striving against sin.
5 And ye have forgotten the exhortation which speaketh unto you as unto children, My son, despise not thou the chastening of the Lord, nor faint when thou art rebuked of him:
6
For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth.
7 If ye endure chastening, God dealeth with you as with sons; for what son is he whom the father chasteneth not?
8 But if ye be without chastisement, whereof all are partakers, then are ye bastards, and not sons.
9 Furthermore we have had fathers of our flesh which corrected us, and we gave them reverence: shall we not much rather be in subjection unto the Father of spirits, and live?
10 For they verily for a few days chastened us after their own pleasure; but he for our profit, that we might be partakers of his holiness.
When does that scourging takes place in verse 6 on those that do not look to Jesus Christ daily to resist sin? After the pre great tribulation rapture event as you compare Hebrews 12;6 with Luke 12:46-48 below for not being ready.
Luke 12: 40 Be ye therefore ready also: for the Son of man cometh at an hour when ye think not.
41 Then Peter said unto him, Lord, speakest thou this parable unto us, or even to all?
42 And the Lord said, Who then is that faithful and wise steward, whom his lord shall make ruler over his household, to give them their portion of meat in due season?
43 Blessed is that servant, whom his lord when he cometh shall find so doing.
44 Of a truth I say unto you, that he will make him ruler over all that he hath.
45 But and if that servant say in his heart, My lord delayeth his coming; and shall begin to beat the menservants and maidens, and to eat and drink, and to be drunken;
46 The lord of that servant will come in a day when he looketh not for him, and at an hour when he is not aware, and will cut him in sunder, and will appoint him his portion with the unbelievers.
47 And that servant, which knew his lord's will, and prepared not himself, neither did according to his will, shall be beaten with many stripes.
48 But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more.
49 I am come to send fire on the earth; and what will I, if it be already kindled?
Note Luke 12:49 as that is before the event when Jesus sends that fire on earth and so those left behind will be on earth for when that fire is sent on earth which infer the event of 1 Corinthians 3:13 below.
1 Corinthians 3:13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.
I remind everyone reading this that 1 Corinthians 3;15 does testifies that those left behind that were not ready are still saved even though they will incur physical death for defiling that temple of God when left behind in that day.
1 Corinthians 3:15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
16 Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
17 If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
The works are burned off of that foundation but that foundation remains as that seal of adoption does too for why those saints & former believers left behind are still saved..