This verse does not say that we can be saved in our sins, and notice that sins are not even mentioned in the context. This is a warning to christians (not sinners) who might not always build their lives on a proper foundation, and sometimes also lack the proper motivation for doing good works.
There are christians who are satisfied by with having a “fire insurance” – an insurance that gives them the right to at least be exempted from hell, as long as they believe in Jesus Christ. They are content with this type of insurance because this means they can still get away with sinning once in a while, and the only thing they would ever risk amounts to reduced rewards in heaven. They might think it’s worth it because heaven is always heaven, and with this type of insurance they can both have their sins and their salvation too. You might exclaim that “true christians wouldn’t reason in that way!”, but isn’t it true that also christians can choose to sin? And isn’t it likely that they might give in for sins more readily if they are being told they won’t end up in hell for it? The tragic thing is that we do NOT have an unconditional fire insurance. We risk to be cut off the vine and thrown in the fire if we lack fruit (John. 15), and we will not reap eternal life in heaven if we break the commandments and sin. If we love Jesus, we obey him (John. 14:15).
The context in 1 Cor. 3:15 shows that it concerns believing christians and their building material and building methods. Sin is nowhere mentioned, and it’s not even needed to be mentioned since we already know from the rest of the Bible that sins separate us from God unless we repent. Nothing unholy shall enter heaven, and sins evidently make us unholy. We can read that the foundation that we build upon must be JESUS CHRIST (and not ourselves, a philosophy, a pastor, a church, a dear friend, money, high status, tradition or someone/something else). It’s the motives in our hearts that will be judged by God. He can see what ground we are building on, and the reasoning in our hearts. Our motive should be to spread the gospel about Jesus Christ in order to see people saved.
Paul is addressing “brethren”, but he is warning these brethren. He also lists a few sins that would make us carnal, and if we are carnal we are not saved:
1 C0r. 3:3 For ye are yet carnal: for whereas there is among you envying, and strife, and divisions, are ye not carnal, and walk as men?
Rom. 8:6 For to be carnally minded is death; but to be spiritually minded is life and peace.
Speaking about christians, Paul says that they shall receive “his own reward” according to their LABOR. This indicates these christians at least do some work, which means they produce some good fruit. That is a good thing because we know that lukewarm christians are not saved. We will reap the reward of eternal life if we show our faith with good works, and we will also be rewarded individually depending on our works.
1 Cor. 8 Now he that planteth and he that watereth are one: and every man shall receive his own reward according to his own labour.9 For we are labourers together with God: ye are God’s husbandry, ye are God’s building.
Revelation 3:16 So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth.
Galatians 6:8 For he that soweth to his flesh shall of the flesh reap corruption; but he that soweth to the Spirit shall of the Spirit reap life everlasting.
Rom. 6:16 Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness?
Paul warns christians that they must take heed on the way they build their lives, and every man’s work shall one day be made manifest. Do we work in order to get a popular position in the society, or because we want to go with the flow? What are our true reasons?
1 Cor.3:10 According to the grace of God which is given unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon. But let every man take heed how he buildeth thereupon.11 For other foundation can no man lay than that is laid, which is Jesus Christ.12 Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble;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.
Paul says “IF any man’s work abide“, meaning it’s not certain it will. It’s still “work”, but will it abide? It depends on the motives. If it abides, the man shall receive both eternal life and individual gratification, but if the work does not abide but burned he will be saved but as by fire. If the man would be sinning on the other hand, he would not even be saved as through fire, but he wouldn’t even be able to enter the kingdom at all. This story is about christians who WORK, in combination with their motives for doing so. Paul ends with a warning to christians that if they defile the temple of God, which they all are, they will be DESTROYED.
1 Cor. 3:14 IF any man’s work abide which he hath built thereupon, he shall receive a reward.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.
Read also the next chapter which is also about the intent of the heart.
1 Cor. 4:5 Therefore judge nothing before the time, until the Lord come, who both will bring to light the hidden things of darkness, and will make manifest the counsels of the hearts: and then shall every man have praise of God.6 And these things, brethren, I have in a figure transferred to myself and to Apollos for your sakes; that ye might learn in us not to think of men above that which is written, that no one of you be puffed up for one against another.
Three chapters later Paul lists sins that will prevent us from entering the kingdom of God, and christians are not exempted:
1 Kor. 6:9 Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind,10 Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God.
We can unfortunately be the cause for that a brother stumbles/falls/is offended, by the way we are living our lives:
1 Kor. 8:12 But when ye sin so against the brethren, and wound their weak conscience, ye sin against Christ.13 Wherefore, if meat make my brother to offend, I will eat no flesh while the world standeth, lest I make my brother to offend. (“stumble” NKJV)