"And the curse, if you do not hearken": From this we can learn that Moses did not command the Jews until his last days when he was about to die and had witnessed all the miracles. Therefore it states "After he had smitten...(Devarim 1:4)".
(Devarim, Ibid. 28) "And the curse, if you do not hearken … and you turn away from the way": from the way of life to the way of death.
"that I command you this day, to go after other gods": From here it was derived: If one acknowledges idolatry, it is as if he denies the entire Torah; and if one denies idolatry, it is as if he acknowledges the entire Torah.