The LORD will not be willing to forgive him, but rather the anger of the LORD and His jealousy will smoke against that man, and the curses written in this book will settle upon him, and the LORD will blot out his name from under heaven. And the LORD will single him out from all the tribes of Israel for calamity, in accordance with all the curses of the covenant written in this Book of the Law. Deuteronomy 29:20-21

paper by Holliewood Studios, barbed wire by Heather Roselli

full passage:

Beware lest there be among you a man or woman or clan or tribe whose heart is turning away today from the LORD our God to go and serve the gods of those nations. Beware lest there be among you a root bearing poisonous and bitter fruit, one who, when he hears the words of this sworn covenant, blesses himself in his heart, saying, ‘I shall be safe, though I walk in the stubbornness of my heart.’ This will lead to the sweeping away of moist and dry alike. The LORD will not be willing to forgive him, but rather the anger of the LORD and his jealousy will smoke against that man, and the curses written in this book will settle upon him, and the LORD will blot out his name from under heaven. And the LORD will single him out from all the tribes of Israel for calamity, in accordance with all the curses of the covenant written in this Book of the Law. Deuteronomy 29:18-21 (Also see Deut. 28:15-68.)

Once again, we're not doing anyone a favor when we "undo" God's warnings to believers (or unbelievers, for that matter). Even though we're living under the New Covenant (Jer. 31:31-34, Luke 22:19-20, 1Cor. 11:23-26, 2Cor. 3:6, Heb. 8:13, 12:22-29), we don't have the authority to promise people who actually despise God's ways and love those of this fallen world that they're "fine" with God. (1John 2:15-17, Jam. 4:4-10, 2Tim. 2:19-26, 2Cor. 6:14-7:1, Col. 3, Eph. 4-5) No one has ever been saved by the works of the law, but only by faith. (Rom. 4:3-5) However, only GOD has the ability to read hearts and minds to see who truly believes and loves Him (Prov. 17:3, Jer. 17:10, Psa. 26:2, Heb. 4:12-13, Rev. 2:21-23, 1Chron. 29:17, 1Cor. 2:9, Jam. 1:12), but we can look for fruits of the Spirit showing whether a person is indwelt and thus, saved--or not. (John 15:1-21, Gal. 5:13-25) Those who truly believe will obey out of love, respect and gratitude. (John 14:15-26, Mark 12:28-34, Rom. 13:8-10, 11-14, 2Cor. 5:14-15, Jam. 1:25, 2:8, 12) We're instructed to examine ourselves to be sure we do possess saving faith. (2Cor. 13:5, Jam. 2:14-26 - these "works" are those of the Holy Spirit, showing that a person IS saved, not TO save them.)

Telling people that God "doesn't see" sin anymore once we come to believe is wrong. God saw the sin of Ananias and Sapphira, who were believers. (Acts 5:1-11, Rom. 16:18, 1Tim. 6:3) Jesus disciplines His people bodily in this life so that they can escape judgment in the next. (1Cor. 11:32, Rev. 3:19) Jesus SAW the sins and shortcomings of the seven churches when He sent His angel to have John write letters to them. (Rev. 2-3) God FORGIVES us of ANY sin when we repent of it--just like we're supposed to do for others. (1John 1:7-10, Rom. 6, Matt. 18:15-35) We don't need to live in fear of being cast off for slipping, or of having to be perfect "or else." But we should have a healthy respect for God as our Father and REPENT when He disciplines us as His children. (1Pet. 1:14-19, 4:1-5, Rom. 16:18-19, Heb. 12:3-4, 5-11, Rom. 8:13-23, 1John 2:28, 3:1, 10) To love the world (that is the things in it, including sin and also loving anyone or anything more than God) is to harden one's heart against God. (Luke 8:11-15, 12:15, Matt. 18:7-9) THAT is dangerous, because it grieves and quenches the Holy Spirit. (Eph. 4:30, 1Thess. 5:19, Heb. 3:12-15, Rom. 2:1-11) How can someone's faith remain strong if they block out the voice of the Holy Spirit? He's the One who gives the gift of faith (not any rituals we do or any amount of "work" we try to perform of our own power). (Eph. 2:8-10, Rom. 10:17, John 6:63)

Let's be sensible and remember that everything in the world will pass away, but after that comes eternity. Let's choose to use our time wisely, KNOWING and serving our great God instead of wasting our time on worthless pursuits. (Eph. 5:15-17, Col. 4:5-6 - but God doesn't want us dictating to other believers exactly what is valuable to Him - Rom. 14, 2Cor. 4:5.) Let's start with reading our own Bibles instead of being satisfied with a few snippets of Scripture per week and letting someone else tell us what the Bible says according to THEIR understanding of it (and possibly to suit their own agenda, and/or to preserve their livelihood). (1Tim. 1:3-11, 2Tim. 3:1-17, 4:1-4, 2Pet. 2:1-3, Jude 1:3-4)

related:

“And to the angel of the church in Sardis write: ‘The words of him who has the seven spirits of God and the seven stars. “‘I know your works. You have the reputation of being alive, but you are dead. Wake up, and strengthen what remains and is about to die, for I have not found your works complete in the sight of my God. Remember, then, what you received and heard. Keep it, and repent. If you will not wake up, I will come like a thief, and you will not know at what hour I will come against you. Yet you have still a few names in Sardis, people who have not soiled their garments, and they will walk with me in white, for they are worthy. The one who conquers will be clothed thus in white garments, and I will never blot his name out of the book of life. I will confess his name before my Father and before his angels. He who has an ear, let him hear what the Spirit says to the churches.’ Revelation 3:1-6

I warn everyone who hears the words of the prophecy of this book: if anyone adds to them, God will add to him the plagues described in this book, and if anyone takes away from the words of the book of this prophecy, God will take away his share in the tree of life and in the holy city, which are described in this book. Revelation 22:18-19 (Also see Prov. 30:5-6.)