This should come as no shock to those who have had some experience wrestling with him, but the Serpent is a sly character. Just look at his tempting of Eve: in one sense, he didn't really say anything that wasn't true (they didn't physically die, they did become like God, knowing good and evil), but in reality, he completely perverted the truth. And it was his questioning of the authority of God to command His creatures that led to the downfall of the human race and the imprisonment of the universe in shackles of death and decay. And this maliciously genius Enemy has been tirelessly working at that same end ever since that day. One of the areas where his influence can be painfully and powerfully felt involves the promised blessings and curses from God toward obedience and disobedience to His commands. Chapters in the Old Testament like Leviticus 26 or Deuteronomy 28 sound downright barbaric to our modern sensibilities. "I'll make you eat your babies"!!?? (Leviticus 26:29) I mean, who says that!? These judgments are harsh! A lot of churchgoing "Christians" don't want to have anything to do with a God like that. It's better to just not read the Old Testament at all (and there are many denominations that don't). No, when bad things happen, these folks would much rather chalk it up to "chance" and let God be the one who says, "There, there", and pats them on the back and makes it all better. He wouldn't do the kinds of things written in those Old Testament books; He's all about love and compassion.
And there we see the Dragon at work yet again. He takes some things that are certainly true about God: His goodness, His compassion, His love, grace, and mercy, and then uses these qualities to question God's authority to judge wickedness. "Did God really say He would destroy you in wrath if you disobeyed? No, that won't happen! He's all about love!"
Those of us who know the tricks of the Accuser would expect this kind of ploy. We might even be used to blocking this punch, but the Devil has another fist, and his use of it goes largely unnoticed. Satan doesn't just attack God's promised curses for disobedience, he also calls into question God's promised blessings for obedience.
The first part of Leviticus chapter 26 and the first part of Deuteronomy 28 both deal with the amazing blessings that God will shower on His people if they obey Him. They are just as beautifully wondrous as the curses are shockingly horrific. There God promises rain in season, increased yield of field and orchard, overabundance of food, peace and security, the absence of dangerous animals from their land, absolute military victory, fruitful child bearing, and even the very presence of God Himself in their midst. These are great things, and even the folks who don't like the Old Testament don't mind reading passages like this. But the place where the Snake has inserted his lie is in the fact that these are blessings for obedience.
"We don't believe in a works-based salvation! It's all of grace!" Such might be the cry of many Christians if you started telling them that they should diligently obey all of God's commands in order to be blessed. The last thing that Satan wants us to believe is that we will be happier and more content if we seek to obey all of God's laws, and so here he has used another deception, confusing our unworthiness to receive the gift of salvation with the Bible's teaching that God expects good works on the part of those who have been saved. It's true that we can't work for salvation. We are dead in our trespasses and sins until God makes us alive together with Christ - quite apart from our own working (Ephesians 2:1-10). But once God has saved us by His grace, He absolutely expects diligent and faithful obedience to His commands out of us (James 1:22).
You see, both of these attacks - attacks against the understanding that God pours out wrath on disobedience and against the understanding that God pours out blessings for obedience - seek to lead us away from a careful attention to God's commands. If something bad happens, it isn't because you disobeyed, and if something good happens, it isn't because you were obedient. We need to throw off this deceit of the Enemy and strive to work hard in obedience to receive God's blessings and avoid His wrath. It is absolutely good and right and biblical to do so.