"See, I am setting before you today a blessing and a curse: the blessing, if you obey the commandments of the LORD your God... and the curse, if you do not obey the commandments of the LORD your God, but turn from the way that I am commanding you today, to follow other gods that you have not known."
Some might call it an ultimatum. Others as a challenge. I think it's simply "the way it is." After receiving God's commandments on Mt. Sinai, God reminded the people of what they now had before them: both a blessing and a curse. If they lived the way God designed them to (relationally with God and others), then life would be a BLESSING! But if they went off on their own & did not live the right way, their lives would feel CURSED. Period.
I really don't see this as a Divine "threat"... but more of a reality check. God's commandments, when seen as a whole, are really about integrity of relationships. When we live in that integrity (with God and others), life is blessed. Why? Because that's how God set things up! When we honor God with our heart & actions... when we treat others with respect & sacred worth... when we are for creation... EVERYTHING & EVERYONE is blessed!!!
Unfortunately, it's human nature to "skew" toward being selfish. We are easily distracted & lose focus. We tend to seek our own interests, benefits, and desires. Those aren't always bad, but often move us away from God's plans for us. Thus, life never seems to be quite right. We miss out on the blessings & joy that God has in store for us.
This doesn't mean that we'll never have problems in life if we follow God's commands... stuff happens to the good an bad all the time. But there will be a sense of blessing even in the struggles, as we do follow God's will. That's a promise! Likewise, when we're wandering off on our own, even if "all is well," it will never quite seem enough. It's the way God "hardwired" us, if you will.
So what'll it be: blessing or curse?