1 Corinthians 3:15…14 If what he has built survives, he will receive a reward. 15 If it is burned up, he will suffer loss. He himself will be saved, but only as if through the flames. 16 Do you not know that you yourselves are God’s temple, and that God’s Spirit dwells in you?…
Remember Ananias and Sapphirah, they lied to the Holy Spirit and God killed them for it. These were two born again believers who were punished as an example for the rest of the church that God hates sin and there will be consequences.
Not every believer who sins dies but some do. God will not stand still for our willful rebellion against Him without consequences.
Acts 5:1-11 "5 But a man named Ananias, with his wife Sapphira, sold a piece of property, 2 and kept back some of the price for himself, with his wife’s [a]full knowledge, and bringing a portion of it, he laid it at the apostles’ feet. 3 But Peter said, “Ananias, why has Satan filled your heart to lie to the Holy Spirit and to keep back some of the price of the land? 4 While it remained unsold, did it not remain your own? And after it was sold, was it not [b]under your control? Why is it that you have [c]conceived this deed in your heart? You have not lied to men but to God.” 5 And as he heard these words, Ananias fell down and breathed his last; and great fear came over all who heard of it. 6 The young men got up and covered him up, and after carrying him out, they buried him."
7 Now there elapsed an interval of about three hours, and his wife came in, not knowing what had happened. 8 And Peter responded to her, “Tell me whether you sold the land [d]for such and such a price?” And she said, “Yes, [e]that was the price.” 9 Then Peter said to her, “Why is it that you have agreed together to put the Spirit of the Lord to the test? Behold, the feet of those who have buried your husband are at the door, and they will carry you out as well.” 10 And immediately she fell at his feet and breathed her last, and the young men came in and found her dead, and they carried her out and buried her beside her husband. 11 And great fear came over the whole church, and over all who heard of these things."
Does this not demonstrate how serious sin against God is and that there will be a come-up-ence either here or at the judgment seat of Christ. No un-confessed sin will go unnoticed by God.
Every believer should be warned about their sin to save them from judgement and loss of rewards later.