Deuteronomy 4:1-40
Therefore watch yourselves very carefully. Since you saw no form on the day that the LORD spoke to you at Horeb out of the midst of the fire, beware lest you act corruptly by making a carved image for yourselves… And beware lest you raise your eyes to heaven, and when you see the sun and the moon and the stars, all the host of heaven, you be drawn away and bow down to them and serve them…
Deuteronomy 4:15-16a,19a
Idolatry.
Idolatry is the sin to avoid. In fact, ultimately, it is the only sin. Oh, sure, we do not commonly think of ourselves as worshiping graven images, and we can identify all sorts of other sins like lying, stealing, murder, adultery, sins of commission, and sins of omission — you name it. But in truth, all other forms of sin are really idolatry in disguise, as they all put something else before God. That “something” does not have to be some object carved from wood or stone. It can be a variety of things, but ultimately that “something” ends up being Self.
So if you think that idolatry fell out of fashion centuries ago, think again. It still strikes all too close to home, hence our need to die every day.
Know therefore today, and lay it to your heart, that the LORD is God in heaven above and on the earth beneath; there is no other.
Deuteronomy 4:39
And [Jesus] said to all, “If anyone would come after Me, let him deny himself and take up his cross daily and follow Me.
Luke 9:23
See also: February 22 / Deuteronomy 3-4