It should go without saying that you won’t improve the Mona Lisa by adding a moustache.
The last book of Moses and the last book of the Bible give us similar warnings: “You shall not add to the word which I command you, nor take from it, that you may keep the commandments of the Lord your God which I command you” (Deut 4:2). John, the apostle of love, rings an even more dire alarm bell: “If anyone adds to these things, God will add to him the plagues that are written in this book; and if anyone takes away from the words of the book of this prophecy, God shall take away his part from the Book of Life, from the holy city, and from the things which are written in this book” (Rev 22:18-19). Adding to the Word is also subtraction. If, for example, you add good works, church sacraments, or law keeping to the finished work of Christ, you actually diminish God’s offer, demolish the basis of assurance, and destroy the simplicity, clarity and certainty of the gospel message. Here are the Savior’s own words—and I take what He says over every theologian—“Most assuredly, I say to you, he who hears My word and believes in Him who sent Me has everlasting life, and shall not come into judgment, but has passed from death into life” (Jn 5:24). Don’t you dare add anything to this! Likewise, God, through Moses, told His people that there was nothing extraneous or unnecessary in what He commanded. And the consequences of obeying or not should be obvious. “Your eyes have seen what the Lord did…for the Lord your God has destroyed from among you all the men who followed Baal of Peor. But you who held fast to the Lord your God are alive today, every one of you” (vv 3-4). We also feel the dying of fellowship and joy within when we disobey. And we know the invigorating power of obedience, too. It’s still a matter of life and death.